The science of low carb and keto
- Weight loss
- Metabolic risk factors
- Heart disease, cholesterol and saturated fats
- Diabetes type 2
- Diabetes type 1
- Liver disease
- Reflux disease
- Intermittent fasting
- Red meat
- External resources
- For doctors
- EB policy
- Evidence policy
Evidence also suggests that natural saturated fats are neutral with regard to health, warnings about the health dangers of red meat are based on very weak evidence, and low-fat diets do not appear to have any special health or weight benefits beyond those of a low-carb diet.1.
Whether low-carb diets are superior for weight loss is still a somewhat controversial topic. Yet looking at the high-quality research to date, it’s clear that on average carbohydrate restriction outperforms low-fat and other diets for weight loss.
A number of meta-analyses of RCTs (considered the strongest, most robust type of evidence) have come to the same conclusion: low-carb diets tend to outperform other diets for weight loss.
Here are two recent examples showing greater weight loss on low-carb diets compared to low-fat diets:
The British Journal of Nutrition 2016: Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomised controlled trials [strong evidence] Learn more
Low carb does not just result in more weight loss than other comparison diets, it also results in more fat loss, especially when carbs are limited to 50 grams per day:
The failure of low fat
A 2015 article in the prestigious journal The Lancet summarizes all major low-fat weight loss scientific trials. The conclusion? There’s no evidence that low-fat helps people lose weight, compared to any other diet advice.
This should cause us to question the commonly held belief that a low-fat diet is right for most people. In fact, people given the opposite advice in studies tended to lose significantly more weight. Learn more
Weight loss and risk factors
A 2012 review of all major trials of low carb diets show both improved weight and improvement of the major risk factors for heart disease:
RCTs showing significantly more weight loss with low-carb diets vs. other diets
There are at least 31 modern scientific studies of the highest quality (RCTs, or randomized controlled trials) that show significantly better weight loss with low-carb diets, according to the latest count by the Public Health Collaboration UK. The number of studies showing the opposite? Zero.
Here are three of the best RCTs to date:
- New England Journal of Medicine 2008: Weight loss with a low-carbohydrate, mediterranean, or low-fat diet [moderate evidence]
This was a two-year trial in which 322 people were randomly assigned to follow a Mediterranean diet, a low-fat diet, or a low-carb diet. By the study’s end, the low-carb group had lost the most weight – even though they were allowed to eat as much low-carb food as they needed to feel satisfied, while the other two groups followed calorie-restricted diets.
- Annals of Internal Medicine 2014: Effects of low-carbohydrate and low-fat diets: a randomized trial [moderate evidence]
In this study, 148 people were randomized to consume a low-carb diet (less than 40 grams per day) or a low-fat diet (less than 30% of daily carbs per day) for one year. In addition to losing 3.5 kg (7.7 lbs) more than the low-fat group, the low-carb group also had greater improvements in HDL cholesterol, triglycerides, and other cardiovascular disease risk factors.
- Journal of the American Medical Association 2007: Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women. The A to Z weight loss study: a randomized trial [moderate evidence]
One of the most well-known weight-loss trials (often referred to as the A to Z study) involved randomizing overweight premenopausal women to eat either a low-carb (Atkins), moderate-carb (Zone), low-fat (Ornish), or low-calorie, portion-controlled (LEARN) diet for one year. At the end of the study, the women in the low-carb group had lost twice as much weight (4.7 kg, or 10.3 lbs) as the Ornish and LEARN groups and nearly three times as much as the women in the Zone group.
28 more RCTs showing more weight loss on low carb
- Nutrition & Diabetes 2017: Twelve-month outcomes of a randomized trial of a moderate-carbohydrate versus very low-carbohydrate diet in overweight adults with type 2 diabetes mellitus or prediabetes [moderate evidence]
- Applied Physiology, Nutrition, and Metabolism 2017: A 12-week low-carbohydrate, high-fat diet improves metabolic health outcomes over a control diet in a randomised controlled trial with overweight defence force personnel [moderate evidence]
- Obesity (Silver Spring) 2017: PROP nontaster women lose more weight following a low-carbohydrate versus a low-fat diet in a randomized controlled trial [moderate evidence]
- Journal of Medical Internet Research 2017: An online intervention comparing a very low-carbohydrate ketogenic diet and lifestyle recommendations versus a plate method diet in overweight individuals with type 2 diabetes: a randomized controlled trial [moderate evidence]
- Diabetes & Metabolic Syndrome 2017: Induced and controlled dietary ketosis as a regulator of obesity and metabolic syndrome pathologies [moderate evidence]
- Clinical Nutrition 2017: A randomized controlled trial of 130 g/day low-carbohydrate diet in type 2 diabetes with poor glycemic control [moderate evidence]
- The Journal of Nutrition 2015: A lower-carbohydrate, higher-fat diet reduces abdominal and intermuscular fat and increases insulin sensitivity in adults at risk of type 2 diabet [moderate evidence]
- PloS One 2014: A randomized pilot trial of a moderate carbohydrate diet compared to a very low carbohydrate diet in overweight or obese individuals with type 2 diabetes mellitus or prediabetes [moderate evidence]
- Journal of Pediatric Endocrinology and Metabolism 2012: Metabolic impact of a ketogenic diet compared to a hypocaloric diet in obese children and adolescents [moderate evidence]
- Obesity (Silver Spring) 2011: Adiponectin changes in relation to the macronutrient composition of a weight-loss diet [moderate evidence]
- The Journal of Pediatrics 2010: Efficacy and safety of a high protein, low carbohydrate diet for weight loss in severely obese adolescents [moderate evidence]
- Lipids 2009: Carbohydrate restriction has a more favorable impact on the metabolic syndrome than a low fat diet [moderate evidence]
- Obesity 2009: Effects of a low carbohydrate weight loss diet on exercise capacity and tolerance in obese subjects [moderate evidence]
- The American Journal of Clinical Nutrition 2008: Effects of weight loss from a very-low-carbohydrate diet on endothelial function and markers of cardiovascular disease risk in subjects with abdominal obesity [moderate evidence]
- Nutrition & Metabolism 2008: The effect of a low-carbohydrate, ketogenic diet versus a low-glycemic-index diet on glycemic control in type 2 diabetes mellitus [moderate evidence]
- American Journal of Clinical Nutrition 2007: Low- and high-carbohydrate weight-loss diets have similar effects on mood [moderate evidence]
- Diabetic Medicine 2007: A low-carbohydrate diet is more effective in reducing body weight than healthy eating in both diabetic and non-diabetic subjects [moderate evidence]
- Diabetic Medicine 2006: Short-term effects of severe dietary carbohydrate-restriction advice in Type 2 diabetes–a randomized controlled trial [moderate evidence]
- Journal of the American Dietetic Association 2005: Perceived hunger is lower and weight loss is greater in overweight premenopausal women consuming a low-carbohydrate/high-protein vs high carbohydrate/low-fat diet [moderate evidence]
- Diabetologia 2005: Comparison of high-fat and high-protein diets with high-carbohydrate diet in insulin-resistant obese women [moderate evidence]
- The Journal of Clinical Endocrinology and Metabolism 2005: The role of energy expenditure in the differential weight loss in obese women on low-fat and low-carbohydrate diets [moderate evidence]
- Archives of Internal Medicine 2004: The national cholesterol education program diet vs a diet lower in carbohydrates and higher in protein and monounsaturated fat. A randomized trial [moderate evidence]
- Nutrition & Metabolism 2004: Comparison of energy-restricted very low-carbohydrate and low-fat diets on weight loss and body composition in overweight men and women [moderate evidence]
- Annals of Internal Medicine 2004: A low-carbohydrate, ketogenic diet versus a low-fat diet to treat obesity and hyperlipidemia. A randomized, controlled trial [moderate evidence]
- The Journal of Nutrition 2004: Very low-carbohydrate and low-fat diets affect fasting lipids and postprandial lipemia differently in overweight men [moderate evidence]
- The Journal of Clinical Endocrinology & Metabolism 2003: A randomized trial comparing a very low carbohydrate diet and a calorie-restricted low fat diet on body weight and cardiovascular risk factors in healthy women [moderate evidence]
- The New England Journal of Medicine 2003: A low-carbohydrate as compared with a low-fat diet in severe obesity [moderate evidence]
- The Journal of Pediatrics 2003: Effects of a low-carbohydrate diet on weight loss and cardiovascular risk factor in overweight adolescents [moderate evidence]
Comment on RCTs
All of the studies above show significantly more weight loss for the group that was advised to eat a low-carb diet (Atkins, in many cases). To the best of our knowledge, the opposite has never been shown: Low carb has never lost a weight loss trial significantly. This means that low carb’s victory record over low fat/low calorie advice is 31-0.
Feel free to let us know of any exceptions (or more examples) by emailing to firstname.lastname@example.org.
RCTs with non-significant results
According to the Public Health Collaboration UK, this is the detailed record for 62 RCTs comparing low-carb to low-fat or low-calorie diets:
- In 53 of the 62 studies, people in the low-carb group lost more weight than those in other diet groups – including the 31 cases above where the difference was statistically significant.
- In 7 of the 62 studies, people in the low-fat or low-calorie diet group lost slightly but insignificantly more weight than those in the low-carb diet group.
- In 2 studies, weight loss was exactly equal in both groups.
Here are a few examples where there were no major differences in weight loss between low-carb and other diets:
Journal of the American Medical Association 2018: Effect of low-fat vs low-carbohydrate diet on 12-month weight loss in overweight adults and the association with genotype pattern or insulin secretion: the DIETFITS randomized clinical trial [moderate evidence]
This recent 12-month study found that people who followed a low-carb or low-fat diet (both with low amounts of sugar or processed carbohydrates) lost a similar amount of weight, on average, regardless of the type of diet they were assigned to and whether it “matched” their genetic insulin response. However, there was a minor, non-significant trend towards more weight loss with low carb, even in this study.
- The American Journal of Clinical Nutrition 2015: Comparison of low- and high-carbohydrate diets for type 2 diabetes management: a randomized trial [moderate evidence]
In this trial of people with type 2 diabetes, both low-carbohydrate and high-carbohydrate diets led to similar weight loss of about 10 kg (22 pounds) within one year.
- Journal of the American Medical Association 2005: Comparison of the Atkins, Ornish, Weight Watchers, and Zone Diets for weight loss and heart disease risk reduction [moderate evidence]
Interestingly, two years before the A to Z study showing that low carb was clearly more effective for weight loss than other diets, a similar study found that weight loss was roughly the same after one year for each of the four diets studied: low-carb, low-fat, Weight Watchers, or Zone.
All 62 RCTs can be found on the Public Health Collaboration website.
Metabolic risk factors
Low carb clearly shows superior results for all the main features of the “metabolic syndrome”, i.e. weight, blood sugar, blood pressure and the cholesterol profile connected to metabolic dyslipidemia (characterized by low HDL and high triglycerides).
Metabolic risk factors are strongly connected to chronic diseases like type 2 diabetes, heart disease, stroke, dementia and even cancer.2 So the fact that we can improve all of them with one single lifestyle intervention (reducing carb intake) could be incredibly important.
Overview of randomized controlled trials
Here’s an overview of the results of dozens of studies and meta-analyses comparing low-carb or low-fat diets, while tracking weight and other risk factors.
The blue (low carb) or red (low fat) squares signify a statistically significant advantage. The pale blue or red squares signify a non-significant trend toward low carb or low fat being superior.
LF %kh = Percent carbohydrate intake in the low-fat group
HDL = High density lipoprotein
TG = Triglycerides
BP = Blood pressure
A1c = HbA1c
fGluc = Fasting glucose
fIns = Fasting insulin level
InsSens = Insulin sensitivity
TC = Total cholesterol
LDL = Low density lipoprotein
However, since all metabolic factors including HDL and TG favor low carb, cholesterol measurements that may have higher predictive value that LDL, such as TG/HDL or TC/HDL ratios, also favor low carb.3
In addition, low carb shows greater improvement in the other important risk factors: blood pressure, blood sugar and weight (including waist measurement).
Links to references
Here are links to all the studies above, ordered from oldest to newest:
Brehm -03, Foster -03, Samaha -03, Sondike -03, Aude -04, Volek -04, Meckling -04, Yancy -04, Stern -04, McAuley -05, Nickols-R -05, Dansinger -05, Daly -06, Truby -06, Gardner -07, Ebbeling -07, Halyburton -07, Dyson -07, Westman -08, Keogh -08, Shai -08, Tay -08, Davis -09, Bradley -09, Volek -09, Sacks -09, Brinkworth -09, Jenkins -09, Frisch -09, Elhayany -10, Iqbal -10, Lim -10, Hernandez -10, Yancy -10, Foster -10, Krebs -10, Goldstein -11, Summer -11, Guldbrand -12, Partsalaki -12, Ruth -13, Yamada -14, Saslow -14, Bazzano -14, Tay -15, Saslow -17, Gardner -18.
Links to the meta-analyses:
The effect of low-carb diets on the cholesterol profile is demonstrated in a recent systematic-review and meta-analysis of RCTs in overweight and obese adults. HDL cholesterol and triglycerides improved the most in those who ate very-low-carbohydrate and ketogenic diets providing less than 50 grams of carbs per day:
Heart disease, cholesterol and saturated fats
Despite half a century of research there is still no evidence that natural saturated fat (like butter, eggs etc.) is anything but neutral from a health perspective.4
In a recent analysis, 19 leading researchers concluded that it’s wrong to maintain the general advice to reduce saturated fat intake, as the evidence no longer supports it.5
Another recent analysis of the field published in BMJ Evidence-Based Medicine concluded that: “The preponderance of evidence indicates that low-fat diets that reduce serum cholesterol do not reduce cardiovascular events or mortality. Specifically, diets that replace saturated fat with polyunsaturated fat do not convincingly reduce cardiovascular events or mortality. These conclusions stand in contrast to current opinion.”6
Have a look at recent systematic reviews of all the evidence.
A 2009 systematic review of cohort studies and RCTs looking at potential relationships between dietary factors and heart disease concluded that “Insufficient evidence of association is present for intake of … saturated or polyunsaturated fatty acids; total fat … meat, eggs and milk”:
Similarly, a 2010 review of cohort studies found “…no significant evidence for concluding that dietary saturated fat is associated with an increased risk of CHD or CVD”:
Similar meta-analyses of observational studies in 2015 and 2017 reached the same conclusions about the lack of association between saturated fat and heart disease:
British Medical Journal 2015: Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies [moderate evidence]
Looking at systematic reviews of RCTs, there is still no convincing evidence that saturated fat is harmful.
In two of these reviews, researchers concluded that replacing saturated fats with unsaturated fats might slightly reduce the risk of heart attack and other cardiovascular events by about 14 to 19 percent:
However, many other more recent systematic reviews of RCTs haven’t shown any reduction in CVD risk as a result of substituting saturated fats with unsaturated fats:
But wait, what about butter and other high-fat dairy specifically? Well, there is some interesting evidence that people consuming it might be, if anything, thinner and healthier than others.
In 2012, researchers exploring the relationship between full-fat dairy, heart health and weight concluded that “the observational evidence does not support the hypothesis that dairy fat or high-fat dairy foods contribute to obesity or cardiometabolic risk”:
Learn more: A user guide to saturated fat
Polyunsaturated fats and the Sydney Diet Heart Study
Advice to replace saturated fats with polyunsaturated fats – to reduce heart disease risk – is controversial and the evidence supporting it is shaky, mostly very old studies with many weaknesses.
A re-evaluation of one of these, the Sydney Diet Heart Study, uncovered previously unpublished data showing an increased risk of death and heart disease in the group getting polyunsaturated omega 6 fats.
When including this data in a meta-analysis of all studies there is an almost significant trend towards increased heart disease and death from heart disease when replacing saturated fats with polyunsaturated omega 6 fats. Certainly, it does not appear to have any health benefits.
British Medical Journal 2013: Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis [strong evidence]
The PURE study
Could a low-fat diet cause more harm than good? A recent large observational study published in the prestigious medical journal The Lancet suggests that low fat, high carb advice may point us in the wrong direction.The PURE study followed over 135,000 people in 18 countries from 5 continents for over seven years.
They found that people who ate the most carbohydrates died earlier. A higher intake of fat, on the other hand, was linked to longer life – regardless of whether the fat was unsaturated or saturated.
Although this is an observational study and therefore cannot prove that eating fewer carbs and more fat extends life, the authors conclude: “Global dietary guidelines should be reconsidered in light of these findings.” Learn more
Hard endpoints on low carb
Most low-carb studies just track risk factors for heart disease, they are not large enough to track hard endpoints like actual health outcomes, e.g. the risk of a heart attack. But there is one RCT study that tracked signs of carotid atherosclerosis during 2 years of advice to eat a low-carb, high-fat diet (Atkins).
The result? There was significant regression of measurable carotid vessel wall volume, implying a reduction of atherosclerosis. There was improvement on other tested diets too, but the non-significant trend was towards a larger improvement on a low-carb diet.
One possible explanation, according to the researchers, was the loss of weight and reduced blood pressure resulting from the change in diet.
Fats, cholesterol and dietary guidelines
Type 2 diabetes
The failure of conventional treatment
Conventional treatment, based on regular lifestyle advice (eat less, run more) and intensive medication regimens have in some ways failed to improve diabetes management. No less than seven randomized controlled trials have demonstrated that diabetes drugs do not reduce heart disease, the major killer of people with diabetes.
Occasionally these trials have even had to be stopped, due to the drugs not just resulting in more weight gain and more side effects, but also resulting in a greater risk of dying than simply letting the blood glucose be high.7
Low carb: systematic reviews
The advantage of a low-carb diet in type 2 diabetes has been recognized in several systematic reviews and meta-analyses or RCTs. Here are two recent examples:
The American Journal of Clinical Nutrition 2018: Effects of low-carbohydrate- compared with low-fat-diet interventions on metabolic control in people with type 2 diabetes: a systematic review including GRADE assessments [strong evidence]
European Journal of Clinical Nutrition 2017: The interpretation and effect of a low-carbohydrate diet in the management of type 2 diabetes: a systematic review and meta-analysis of randomised controlled trials [strong evidence]Here’s another review of the evidence behind low carb in the treatment of type 2 diabetes, written by experts who are generally in favor of the idea:
Here are five RCTs demonstrating the benefits of low-carbohydrate diets in people with type 2 diabetes:
Nutrition & Diabetes 2017: Twelve-month outcomes of a randomized trial of a moderate-carbohydrate versus very low-carbohydrate diet in overweight adults with type 2 diabetes mellitus or prediabetes [moderate evidence]
A study of a keto low-carb diet from Virta Health, involving about 330 people, found that at the one-year mark 97 percent of patients had reduced or stopped (!) their insulin use. Furthermore, 58 percent no longer had a diabetes diagnosis, i.e. they had reversed their disease.
These results falsify the idea that the disease is chronic, progressive, and irreversible. It’s a reversible disease, when using an effective lifestyle treatment. Read more
Frontiers in Endocrinology 2019: Long-term effects of a novel continuous remote care intervention including nutritional ketosis for the management of type 2 diabetes: A 2-year non-randomized clinical trial [weak evidence]The longest published study yet on low carb for type 2 diabetes, is a non-randomized intervention trial of a 20% carbohydrate diet for people with obesity and type 2 diabetes. They published a 44-month followup showing continued good results on A1c, weight and reduction of diabetes medications:
Learn more: How to reverse type 2 diabetes
Type 2 diabetes
Type 1 diabetes
The authors of a recent systematic review of low-carbohydrate diets in type 1 diabetes concluded that there is an urgent need for additional randomized controlled trials and other high-quality studies in this area:
It’s clear that compared with the robust evidence supporting low-carb and ketogenic diets for type 2 diabetes, research on carb restriction for type 1 diabetes is sadly lacking. However, as we await the results of RCTs currently in progress, here are some encouraging results from existing studies on low-carb diets in people with type 1 diabetes.
Controlled studies have shown that people with type 1 diabetes who limit carbs to 50 or 100 grams per day experience more stable blood sugar and fewer episodes of hypoglycemia compared to type 1’s who eat a higher-carb diet — with a nice bonus of weight loss in those who are overweight:
Diabetes, Obesity and Metabolism 2017: Short-term effects of a low-carbohydrate diet on glycaemic variables and cardiovascular risk markers in patients with type 1 diabetes: a randomized open-label crossover trial [moderate evidence]
Asia Pacific Journal of Clinical Nutrition 2016: A randomised trial of the feasibility of a low-carbohydrate diet vs standard carbohydrate counting in adults with type 1 diabetes taking body weight into account [moderate evidence]
There are also some non-controlled studies that, while considered weak evidence, demonstrate excellent “real world” results for people with type 1 diabetes who follow a low-carbohydrate diet long term.
This study demonstrates that type 1 diabetes patients who go on a low-carb, high-protein diet on average achieve truly great results, with low rates of major complications, and children who followed it for years did not show any signs of impaired growth. Learn more
Type 1 diabetes
Long-term safety of low carb
There are many myths and fears about the long-term effects of low carb. However, no firm evidence of any real risks exist, to the best of our knowledge. Instead, many of these fears have been disproven.
There has been a lot of worry from some people about the perceived risks of protein intake on the acid-base balance of the body, and how that could affect the bones. The evidence shows this is a myth. The internal pH of the body (in the blood) is firmly regulated and it is not significantly affected by what we eat.9
Regarding bone health, the latest meta-analysis endorsed by the International Osteoporosis Foundation makes the situation very clear: “There is no evidence that diet-derived acid load is deleterious for bone health. Thus, insufficient dietary protein intakes may be a more severe problem than protein excess in the elderly.”
Ketogenic diets have been studied extensively in people with epilepsy. In fact, they are often recommended for those who either fail to respond to anti-seizure medications or can’t tolerate their side effects.
A large review of 16 studies in adults with uncontrolled epilepsy found that ketogenic diets were well-tolerated long term and typically resulted in significantly fewer seizures – or even complete freedom from seizures in a minority of cases:
Epilepsy Research 2016: Evaluation of a simplified modified Atkins diet for use by parents with low levels of literacy in children with refractory epilepsy: a randomized controlled trial [moderate evidence]
Can low carb help reverse a fatty liver? A team of Swedish researchers published a 2017 study in the journal Cell Metabolism. Obese subjects suffering from non-alcoholic fatty liver disease (NAFLD) followed a low-carbohydrate diet without restricting calories.
Lead author Jan Boren of the University of Gotheburg reported some fantastic effects of carbohydrate restriction on liver fat:
“We observed rapid and dramatic reductions of liver fat and other cardiometabolic risk factors and revealed hitherto unknown underlying molecular mechanisms.”
Given the strong connection to excess weight, high insulin levels and other metabolic problems, a low-carb diet should be ideal for reversing polycystic ovary syndrome (PCOS). In fact, the low-carb diet is the only treatment that consistently and reliably lowers insulin levels and reverses the metabolic issues that include PCOS. Therefore, a low-carb diet should be the core of any effective treatment for PCOS.
Although long term, high quality studies have not been done, the limited available science shows great promise:
- One small 2005 study followed 11 women with PCOS as they went on a ketogenic low-carb diet for six months. The 5 women who completed the study greatly improved their weight, hormonal status and perceived amount of body hair. Two of them became pregnant despite previous infertility problems:
Nutrition & Metabolism 2005: The effects of a low-carbohydrate, ketogenic diet on the polycystic ovary syndrome: a pilot study [weak evidence]
- In a 2015 study, 24 women with PCOS who ate diets containing roughly 70 grams of net carbs per day for 12 weeks had significant reductions in insulin levels, insulin resistance, triglycerides and testosterone, along with losing an average of 19 pounds (8.6 kg) by the end of the study:
- Studies in 2006 and 2013 showed that even a very modest reduction in carbohydrates (from 55 to 41 percent of energy) can result in significant improvements in weight, hormones and risk factors for women with PCOS:
Fertility & Sterility 2006: Role of diet in the treatment of polycystic ovary syndrome [weak evidence]
- Finally, a 2017 review of relevant studies finds that low-carbohydrate diets tend to “reduce circulating insulin levels, improve hormonal imbalance and resume ovulation to improve pregnancy rates”.
Nutrients 2017: The effect of low-carbohydrate diets on fertility hormones and outcomes in overweight and obese women: a systematic review [systematic review of randomized and nonrandomized trials; weak evidence]
Beyond the scientific evidence cited above, the clinical experience of doctors using it strongly support low carb as an effective treatment for PCOS:
In 2009 a US team at the University of North Carolina, that included Dr. Eric Westman, specifically examined a very low-carb diet — less than 20 g of carbs a day — for IBS. During the study, 13 people with diarrhea-predominant IBS started with a standard American diet for two weeks, then switched to a very low-carb diet for four weeks; 10 out of the 13 subjects (77%) had significant improvements, with the very low-carb diet improving their abdominal pain, reducing their diarrhea and improving their quality of life:
In recent years, a specific diet developed in Australia, called the low FODMAP diet, has been getting a lot of research attention, with some studies showing 75 per cent of people with diagnosed IBS had their symptoms improve on it. FODMAP is an acronym for fermentable oligosaccharides, disaccharides, monosaccharide’s and polyols. That unwieldy name describes types of short-chain carbohydrates found in many fruits, vegetables, legumes, grains, dairy products and some processed foods.
European Journal of Nutrition 2016: Does a diet low in FODMAPs reduce symptoms associated with functional gastrointestinal disorders? A comprehensive systematic review and meta-analysis [moderate evidence]
Inflammatory bowel disease
Plenty of anecdotal reports support that a low-carb or low-carb Paleo diet may reduce symptoms of inflammatory bowel diseases like Crohns’ disease or ulcerative colitis (examples: 1, 2). To our knowledge there is not yet any controlled trials.
Here’s a published case report:
Reflux disease / heartburn
At least two studies show promising effects of a low-carb diet on reflux disease.
In a small trial of eight obese people with GERD, consuming a ketogenic diet containing less than 20 grams of carbs per day led to normalization of esophageal pH levels (indicating a less acidic environment in the esophagus) after just 6 days on the diet. In addition, the participants reported improvements in chest burning and discomfort, belching, and other symptoms of reflux.
Alimentary Pharmacology and Therapeutics 2016: Dietary carbohydrate intake, insulin resistance and gastro‐oesophageal reflux disease: a pilot study in European‐ and African‐American obese women [weak evidence]
Is it possible to avoid migraines by avoiding carbs? Studies and practical experience suggest it might be. There are at least two promising studies so far.
- Euroupean Journal of Neurology 2015: Migraine improvement during short lasting ketogenesis: a proof-of-concept study [weak evidence]
- Journal of Headache and Pain 2016: Cortical functional correlates of responsiveness to short-lasting preventive intervention with ketogenic diet in migraine: a multimodal evoked potentials study [weak evidence]
Limited evidence (such as animal studies and case reports) suggests that low-carb diets might be helpful for some people with ADHD and other somewhat related conditions like OCD and Tourette’s syndrome.
One small study has found improvement in memory in people with mild cognitive impairment, using a ketogenic diet:
Ketogenic diets provide an alternative fuel source for the brain, which may be of benefit to people with dementia or other cognitive issues. Clinical trials in patients with Alzheimer’s or cognitive impairment have shown that even though their brains can’t use glucose effectively, they may have a similar capacity to use ketones as the brains of healthy older people:
Annals of the New York Academy of Sciences 2016: Can ketones compensate for deteriorating brain glucose uptake during aging? Implications for the risk and treatment of Alzheimer’s disease [overview article]
A recent eight-week RCT found that people with Parkinson’s disease who ate a ketogenic diet had greater improvement in symptoms than those who ate a low-fat diet:
This small pilot study of five people with Parkinson’s disease showed an improvement of symptoms on a ketogenic diet. There was no control group, so a placebo effect can’t be ruled out:
Aside from a few case studies, there isn’t yet much more published research in this area.
Similar to research on Parkinson’s disease, high-quality evidence for benefits of carbohydrate restriction in multiple sclerosis is extremely limited. Beyond occasional positive anecdotal reports, there is some emerging clinical research.
A 2015 study reported that MS patients who followed a ketogenic diet or fasted for several days experienced significant improvements in quality of life scores and triglyceride levels:
European Committee For Treatment and Research in Multiple Sclerosis 2015: Ketogenic diet and prolonged fasting improve health-related quality of life and lipid profiles in multiple sclerosis – a randomized controlled trial [moderate evidence]
A small pilot study in 20 people with relapsing MS demonstrated lack of progression of their disease for 6-months while following a ketogenic diet. While this is preliminary data that needs larger confirmatory studies, it raises the possibility that a ketogenic diet might have a role in MS treatment:
There seems to be a connection between fibromyalgia and insulin resistance, high blood sugar and type 2 diabetes. Since low-carb diets often are effective versus the latter conditions, a positive effect on fibromyalgia could be possible. Learn more
It’s not unusual for people to combine a low-carb diet with intermittent fasting, either for convenience or to improve the effectiveness of weight loss or diabetes reversal.
A common variant of intermittent fasting is called 16:8, meaning you fast for 16 hours per day. This is often achieved by skipping breakfast. This can improve weight loss results.10
Intermittent fasting appears to be a promising alternative to continuous calorie restriction:
Low carb and the environment
Low-carb diets are often accused of being environmentally unsustainable, due to the impact of meat production. This is wrong for two reasons. First of all, a low-carb or keto diet should only be moderate in protein (like meat), with most of the energy coming from fat.11 It’s even possible to eat a vegetarian low-carb diet.
Secondly, the environmental impact of meat production is highly variable. Even the production of beef – usually considered by far the worst from a climate perspective – can be handled in an environmentally friendly way.
A 2018 study demonstrates that properly managed livestock can be made climate neutral or even carbon-negative, meaning more carbon is stored in soil than is released into the atmosphere:
Learn more: The green keto meat eater, part 1
Red meat and health
Red meat is often claimed to have negative health consequences, even including an increased risk of cancer. However, these claims are backed mostly by weak epidemiological studies (statistical correlation with very low odds ratios around 1.2).
Most epidemiological findings like this turn out to be false when they are tested in rigorous intervention trials.
Plus, not all observational trials agree that there is an increased risk. A 2019 review and meta-analysis of cohort studies found very low quality of evidence to suggest any increased cancer risk from red meat.12
Not surprisingly, when the theory that red meat causes disease like cancer has been tested in interventional trials, it has not held up. A good example is the Polyp Prevention Trial, that tested a low-fat, low-meat diet on over 2,000 people for 8 years to see if it could prevent colorectal cancer. The result? There was no benefit to reducing meat.
- Cancer Epidemiology, Biomarkers & Prevention 2007: The polyp prevention trial continued follow-up study: no effect of a low-fat, high-fiber, high-fruit, and -vegetable diet on adenoma recurrence eight years after randomization [moderate evidence]
- Journal of the American Medical Association 2006: Low-fat dietary pattern and risk of colorectal cancer [moderate evidence]
In addition, a review of RCTs comparing a lower vs. higher red meat consumption used the GRADE system to quantify the strength of the evidence. The authors concluded there is no meaningful increase in cancer or heart disease with higher red meat consumption.14Learn more: Guide to red meat – is it healthy?
Salt and health
According to many health organizations, most people should cut back on sodium – often to below 2.3 grams per day – in order to prevent high blood pressure and other health problems. On high-carb diets, this might possibly be beneficial for some. However, on a low-carb diet, people’s sodium needs may actually increase, due to increased losses via the kidneys.15
A 2014 Cochrane review found no increased mortality risk with high sodium intake, and found inconsistent to minimal increased cardiovascular disease risk:
That is in contrast to another review of RCTs that found reduced salt intake did improve all-cause mortality and cardiovascular mortality:
Annals of Internal Medicine 2019: Effects of nutritional supplements and dietary interventions on cardiovascular outcomes: An umbrella review and evidence map [systematic review of RCTs; strong evidence]
The inconsistent data makes it difficult to draw strong conclusions, and makes definitive recommendations to severely lower sodium intake suspect for the general population.
Furthermore, the population-wide advice to cut salt intake to very low levels is also questioned by the six recent studies and one older study (see below) that have shown no clear benefit or possibly even an increased mortality associated with lower salt intakes.
It seems like an intake below about 5 grams of sodium per day may be associated with a shorter average life, according to the studies below. This does not prove causation, as it’s just observational data.
The seven studies
- Journal of the American Medical Directors Association 2018: Association between sodium excretion and cardiovascular disease and mortality in the elderly: a cohort study [very weak evidence]
- Journal of the American Medical Association 2016: Sodium excretion and the risk of cardiovascular disease in patients with chronic kidney disease [very weak evidence]
Here the risk was J-shaped with an increased risk over about 4-5 grams of sodium per day. People with kidney disease may be more sensitive to higher salt intakes, but even for them the tolerance seems way higher than the recommended intakes.
- Lancet 2016: Associations of urinary sodium excretion with cardiovascular events in individuals with and without hypertension: a pooled analysis of data from four studies [very weak evidence]
In this study, consuming more than 7 grams of sodium per day was associated with increased risk of heart attack and death in people with hypertension, while consuming less than 3 grams of sodium per day was associated with increased risk in both people with normal blood pressure and those with hyptertension.
- Journal of the American Medical Association 2011: Fatal and nonfatal outcomes, incidence of hypertension, and blood pressure changes in relation to urinary sodium excretion [very weak evidence]
- Diabetes Care 2011: Dietary salt intake and mortality in patients with type 2 diabetes [very weak evidence]
- Diabetes Care 2011: The association between dietary sodium intake, ESRD, and all-cause mortality in patients with type 1 diabetes [very weak evidence]
- Hypertension 1995: Low urinary sodium is associated with greater risk of myocardial infarction among treated hypertensive men [weak evidence]
External resources about the science of low carb
The science of low carb
Here is the opinion of an expert on low-carb diet research, Dr. William Yancy.
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The Lancet. Diabetes and Endocrinology 2015: Effect of low-fat diet interventions versus other diet interventions on long-term weight change in adults: a systematic review and meta-analysis [strong evidence] ↩
In addition to saturated fat getting a green light from cardiologists like Dr. Bret Scher, Dr. Scott Murray and Dr. Blair O’Neill, even the Academy of Nutrition and Dietetics has publicly stated that saturated fat should no longer be considered a nutrient of concern, based on the lack of evidence connecting it to heart disease. ↩
Evidence strength downgraded due to lack of high-quality studies. ↩
This includes diets in which very few carbs are consumed, such as ketogenic diets.
However, not every study on breakfast skipping shows increased weight loss. Here’s one negative trial:
In LCHF studies that have shown health benefits, people are usually advised to eat a moderate amount of protein and as much fat as needed to feel satisfied.
Applied Physiology, Nutrition and Metabolism 2017: A 12-week low-carbohydrate, high-fat diet improves metabolic health outcomes over a control diet in a randomised controlled trial with overweight defence force personnel [moderate evidence] ↩
Annals of Internal Medicine 2019: Reduction of Red and Processed Meat Intake and Cancer Mortality and Incidence: A Systematic Review and Meta-analysis of Cohort Studies. [meta-analysis of cohort studies; weak evidence] ↩
Another publication details how there was also no benefit in preventing breast cancer:
Journal of the American Medical Association 2006: Low-fat dietary pattern and risk of invasive breast cancer: the Women’s Health Initiative Randomized Controlled Dietary Modification Trial. [moderate evidence] ↩
Annals of Internal Medicine 2019: Effect of Lower Versus Higher Red Meat Intake on Cardiometabolic and Cancer Outcomes: A Systematic Review of Randomized Trials. [systematic review of randomized trials; strong evidence] ↩
Although the precise mechanism for this isn’t entirely known, some researchers have suggested that when insulin levels are very low (as they typically are on a keto diet), the kidneys may absorb less sodium and excrete more into the urine.