The science of low carb
The page below summarizes the core scientific evidence behind low-carb and keto diets. While these diets are still somewhat controversial, there is now high-quality evidence to support their routine use for weight loss and metabolic disease (e.g. type 2 diabetes, high blood pressure) and certain other conditions.
There’s also good evidence to suggest that the fear of natural saturated fats has been a mistake, and that there’s no general health or weight benefits of a low-fat diet.
- Weight loss
- Metabolic risk factors
- Heart disease, cholesterol and saturated fats
- Diabetes type 2
- Diabetes type 1
- Long-term safety of low carb
- Liver disease
- Low carb and the environment
- Red meat and health
- External resources about the science of low carb
- Low carb for doctors
- More about how low carb works
Some people still claim that weight loss studies do not show any advantage for low carb diets. Unbelievably enough, that is what many so called experts still believe. It’s either ignorance or science denial.
There are at least 31 modern scientific studies of the highest quality (RCT) that show significantly better weight loss with low carb diets. This according to the latest count by the Public Health Collaboration UK. The number of studies showing the opposite? Zero.
RCTs showing significantly more weight loss with low carb diets
- Shai I, et al. Weight loss with a low-carbohydrate, mediterranean, or low-fat diet. N Engl J Med 2008;359(3);229–41.
- Bazzano L, et al. Effects of Low-Carbohydrate and Low-Fat Diets: A Randomized Trial. Ann Intern Med. 2014;161(5):309-318.
- Gardner CD, et al. 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. JAMA. 2007;297:969–977.
- Brehm BJ, et al. 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. J Clin Endocrinol Metab 2003;88:1617–1623.
- Samaha FF, et al. A Low-Carbohydrate as Compared with a Low-Fat Diet in Severe Obesity. N Engl J Med 2003;348:2074–81.
- Sondike SB, et al. Effects of a low-carbohydrate diet on weight loss and cardiovascular risk factor in overweight adolescents. J Pediatr. 2003 Mar;142(3):253–8.
- Aude YW, et al. The National Cholesterol Education Program Diet vs a Diet Lower in Carbohydrates and Higher in Protein and Monounsaturated Fat. A Randomized Trial. Arch Intern Med. 2004;164:2141–2146.
- Volek JS, et al. Comparison of energy-restricted very low-carbohydrate and low-fat diets on weight loss and body composition in overweight men and women. Nutrition & Metabolism 2004, 1:13.
- Yancy WS Jr, et al. A Low-Carbohydrate, Ketogenic Diet versus a Low-Fat Diet To Treat Obesity and Hyperlipidemia. A Randomized, Controlled Trial. Ann Intern Med. 2004;140:769–777.
- Nichols-Richardsson SM, et al. 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. J Am Diet Assoc. 2005;105:1433–1437.
- Krebs NF, et al. Efficacy and Safety of a High Protein, Low Carbohydrate Diet for Weight Loss in Severely Obese Adolescents. J Pediatr 2010;157:252-8.
- Summer SS, et al. Adiponectin Changes in Relation to the Macronutrient Composition of a Weight-Loss Diet. Obesity (Silver Spring). 2011 Mar 31. [Epub ahead of print]
- Halyburton AK, et al. Low- and high-carbohydrate weight-loss diets have similar effects on mood but not cognitive performance. Am J Clin Nutr 2007;86:580–7.
- Dyson PA, et al. A low-carbohydrate diet is more effective in reducing body weight than healthy eating in both diabetic and non-diabetic subjects. Diabet Med. 2007 Dec;24(12):1430-5.
- Keogh JB, et al. Effects of weight loss from a very-low-carbohydrate diet on endothelial function and markers of cardiovascular disease risk in subjects with abdominal obesity. Am J Clin Nutr 2008;87:567–76.
- Volek JS, et al. Carbohydrate Restriction has a More Favorable Impact on the Metabolic Syndrome than a Low Fat Diet. Lipids 2009;44:297–309.
- Partsalaki I, et al. Metabolic impact of a ketogenic diet compared to a hypocaloric diet in obese children and adolescents. J Pediatr Endocrinol Metab. 2012;25(7-8):697-704.
- Daly ME, et al. Short-term effects of severe dietary carbohydrate-restriction advice in Type 2 diabetes–a randomized controlled trial. Diabet Med. 2006 Jan;23(1):15–20.
- Westman EC, et al. The effect of a low-carbohydrate, ketogenic diet versus a low- glycemic index diet on glycemic control in type 2 diabetes mellitus. Nutr. Metab (Lond.)2008 Dec 19;5:36.
The first 17 studies in the list are weight loss trials, the last two are studies on type 2-diabetics (usually overweight) showing the same effect. Many of the studies are of six months or one year duration, one of them (Shai et al) is two years long.
All of these studies show significantly more weight loss for the group that were advised to eat a low carb diet (Atkins, in most cases).
As far as I know the opposite has never been shown: low carb has never lost a weight loss trial significantly. This means that low carb is winning versus the failed low fat/low calorie advice by 19-0!
Feel free to let me know of any exceptions (or more examples) in the comments.
Addition – yet another study with similar results, this time on overweight people with type 2 diabetes:
Saslow S, et al. 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. Nutrition & Diabetes 7, Article number: 304 (2017).
Several meta-analyses of relevant trials have come to the same conclusion as the individual trials above.
- Low carb best for weight loss in yet another new meta analysis
- Low-carb diet best for weight loss, according to yet another new review
Low carb does not just result in more weight loss than other comparison diets, it also results in more fat loss:
Hashimoto Y, et al. Impact of low-carbohydrate diet on body composition: meta-analysis of randomized controlled studies. Obes Rev. 2016 Apr 5. doi: 10.1111/obr.12405. [Epub ahead of print]
Here’s another new meta-analysis showing more weight loss on low carb:
Mansoor N, et al. Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomised controlled trials. Br J Nutr. 2016 Feb 14;115(3):466-79.
The failure of low fat
A recent article in the prestigious journal The Lancet summarizes all major scientific trials on losing weight on low fat. The conclusion? There’s no evidence that low-fat helps to lose weight, compared to any other diet advice.
The latest review of all major trials of low carb diets show improved weight AND improvement of all major risk factors for heart disease:
- Santos FL, et al. Systematic review and meta-analysis of clinical trials of the effects of low carbohydrate diets on cardiovascular risk factors. Obes Rev. 2012 Aug 21. doi: 10.1111/j.1467-789X.2012.01021.x. [Epub ahead of print]
Metabolic risk factors
Low carb clearly shows superior results for all the common features of the “metabolic syndrome”, i.e. weight, blood sugar, blood pressure and the cholesterol profile connected to metabolic dyslipidemia (HDL and triglycerides).
These factors are strongly connected to the risk of chronic disease like type 2 diabetes, heart disease, stroke, dementia and even cancer. So the fact that we can improve all of them with one single lifestyle intervention (reducing carb intake) is clearly 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.
As you can see above, low carb diets repeatedly beat low fat in all metabolic factors. On the other hand, low fat can result in somewhat lower total and LDL cholesterol.
However, since all the metabolic factors (including HDL) favor low carb, even the best measurements of cholesterol-associated risk (like total cholesterol/HDL) favor low carb, on top of the clear victory in blood pressure, blood sugar and weight (including waist measurements).
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:
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 completely safe to eat.
Have a look at these recent reviews of all the evidence:
Insufficient evidence of association is present for intake of … saturated or polyunsaturated fatty acids; total fat … meat, eggs and milk.
- Mente A, et al. A systematic review of the evidence supporting a causal link between dietary factors and coronary heart disease. Arch Intern Med. 2009 Apr 13;169(7):659-69.
There were no clear effects of dietary fat changes on total mortality or cardiovascular mortality…
- Hooper L, et al. Reduced or modified dietary fat for preventing cardiovascular disease. Cochrane Database Syst Rev. 2011 Jul 6;(7):CD002137.
…no significant evidence for concluding that dietary saturated fat is associated with an increased risk of CHD or CVD.
- Siri-Tarino PW, et al. Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease. Am J Clin Nutr. 2010 Mar;91(3):535-46.
But wait, what about butter and other high fat dairy specifically? Well, actually people consuming it are if anything thinner and healthier than others:
The observational evidence does not support the hypothesis that dairy fat or high-fat dairy foods contribute to obesity or cardiometabolic risk…
- Kratz M, et al. The relationship between high-fat dairy consumption and obesity, cardiovascular, and metabolic disease. European Journal of Nutrition, Online First™, 18 July 2012
Yet another meta-analysis:
Harcombe Z, et al. Evidence from prospective cohort studies does not support current dietary fat guidelines: a systematic review and meta-analysis. Br J Sports Med. 2017 Dec;51(24):1743-1749.
This means that the scientific foundation of the low fat dietary advice has fallen. The reasons for it today are mainly economical (low fat high sugar products are very lucrative and finances a lot of lobbying), combined with old-fashioned prestige and inertia.
The low fat dietary advice has become a house of cards with nothing to support it. It is just a question of time before it’s apparent to everybody.
Polyunsaturated fats and the Sidney Diet Heart Study
Advice to replace saturated fats with polyunsaturated – to reduce heart disease risk – is controversial and the evidence is shaky, mostly very old studies with many weaknesses. A re-evaluation of one of these, the Sidney 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.
The PURE study
Could a low-fat diet kill you? A recent study published in the prestigeous medical journal The Lancet is another nail in the coffin for our current fat-phobic, carb-heavy guidelines.The PURE study followed over 135,000 people in 18 countries from 5 continents for over seven years.
They found that people who ate more carbohydrates died earlier. A higher intake of fat, on the other hand, was linked to longer lives. This was true regardless of whether the fat was unsaturated or saturated – high consumption of all fats were linked to a longer life.
The Lancet study concludes: 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. 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:
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 of blood glucose levels have failed miserably. No less than seven randomised controlled trials have proven these drugs do not reduce heart disease, the major killer of people with diabetes.
Sometimes 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 killing more people than simply letting the blood glucose be high (NEJM 2008).
Low carb: Meta-analyses
Meta-analysis from 2017 finds that low-carb diet results in reduced need of medication AND improved health markers (HbA1c, HDL, triglycerides and blood pressure). They conclude that: “Reducing dietary carbohydrate may produce clinical improvements in the management of type 2 diabetes.”:
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
A study of a keto low-carb diet from Virta Health, involving about 330 people, demonstrate that at the 1-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 completely falsifies the idea that the disease is chronic and progressive, and irreversible. It’s a reversible disease, when using an effective lifestyle treatment. Read more
Type 2 diabetes
Type 1 diabetes
This study demonstrates that type 1 diabetic 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. This is clearly a myth. The internal pH of the body (in the blood) is firmly regulated and it is not significantly affected by what we eat.
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.”
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 PCOS. 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.
Indeed, 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.1
- A 2013 study shows 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.2
- 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”.3
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 20g 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.
One small study has found improvement in memory in people with mild cognitive impairment, using a ketogenic diet:
- Krikorian, R et al. Dietary ketosis enhances memory in mild cognitive impairment. Neurobiology of Aging, 2012.
There are studies linking high, or even “normal”, non-diabetic blood sugar levels to dementia and Alzheimer’s. Since a ketogenic diet lowers blood glucose it could conceivably cut the risk of developing these diseases. Take a look at this study for instance:
Crane, Paul K. et al. Glucose Levels and Risk of Dementia. The New England Journal of Medicine, 2013.
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. 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 demonstrate 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:
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 by nothing more convincing than epidemiological studies (statistical correlations) with extremely weak links (e.g. odds ratios around 1.2).
Most epidemiological findings like this turn out to be false when they are tested in rigorous intervention trials.
Not surprisingly, when the theory that red meat causes disease like cancer has been tested in interventional trials, it has completely failed. 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? It did not work at all.
Cancer Epidemiol Biomarkers Prev. 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.
Another great example is the giant Women’s Health Initiative. Half of nearly 49,000 women were randomized to 8 years on a low-fat diet, with significantly less red meat. There was zero positive effect on colorectal cancer (in fact, the trend was towards a slightly higher risk in the intervention group).
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.
Furthermore, the population-wide advice to cut salt intake to very low levels is seriously questioned today. At least six recent studies (see below) have showed no clear benefit or possibly even an increased mortality with lower salt intakes.
It seems like an intake below about 5 grams of sodium per day may lead to a shorter average life.
The six studies
- JAMA 2011: Fatal and Nonfatal Outcomes, Incidence of Hypertension, and Blood Pressure Changes in Relation to Urinary Sodium Excretion
- Hypertension 1995: Low Urinary Sodium Is Associated With Greater Risk of Myocardial Infarction Among Treated Hypertensive Men
- JAMDA 2018: Association Between Sodium Excretion and Cardiovascular Disease and Mortality in the Elderly: A Cohort Study
- JAMA 2016: Sodium Excretion and the Risk of Cardiovascular Disease in Patients With Chronic Kidney Disease – 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.
- Diabetes Care 2011: Dietary Salt Intake and Mortality in Patients With Type 2 Diabetes
- Diabetes Care 2011: The Association Between Dietary Sodium Intake, ESRD, and All-Cause Mortality in Patients With Type 1 Diabetes
External resources about the science of low carb
Update an expert
It’s not OK for “experts” to keep denying all these modern trials. It’s time for them to take the science seriously.
Feel free to copy or link to this list, if you encounter an expert who needs an update.
The science of low carb
Here is the opinion of a true expert on low-carb diets, Dr. William Yancy.
Keep reading about success stories on low carb
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These two publications are both from the same study:
- Clinical Endocrinology 2013: Favourable metabolic effects of a eucaloric lower-carbohydrate diet in women with PCOS
- Metabolism 2014: Effects of a eucaloric reduced-carbohydrate diet on body composition and fat distribution in women with PCOS