Patients with pre-existing health issuesIn general, low-carb and keto diets are safe for most individuals. As we will describe in this guide, certain pre-existing medical conditions may require extra attention and consideration, but they do not preclude carbohydrate restriction.
First, we will discuss the few situations that are not compatible with a low-carb diet. After that, we will explore the medical conditions in which carbohydrate restriction can be employed using careful judgment and consideration.
Conditions incompatible with carbohydrate restriction
Advanced renal disease
Patients with advanced renal disease who are not yet on dialysis usually need low-protein diets that are largely incompatible with carbohydrate restriction.1 It’s not that it can’t be used, but it is enough of a challenge that we do not recommend it.
Rare genetic disorders
Certain rare disorders of fat metabolism are also contraindications to very-low-carb diets.2 These include carnitine palmitoyltransferase (CPT) deficiency; short-chain, medium-chain, or long-chain acyl dehydrogenase deficiency (SCAD, MCAD or LCAD); and pyruvate carboxylase deficiency. Fortunately, these are very rare conditions that are usually diagnosed at a young age. Adult patients are unlikely to present without a pre-existing diagnosis of these severe fat metabolism disorders.
From a lipid standpoint, hyperchylomicronemia and lipoprotein lipase deficiency are contraindications due to the inability to properly carry out fat digestion and metabolism. These conditions likewise usually present early in life, and it is rare to encounter a new diagnosis as an adult. However, if you are caring for a patient with very high triglyceride levels (above 800 mg/dL), you may want to consider specialized evaluation prior to increasing the amount of fat in the diet.
Certain critical and unstable conditions
Patients presenting with critical and unstable medical conditions — such as acute pancreatitis, acute liver failure, gout attacks, and others — are not candidates for an immediate start of a low-carbohydrate dietary intervention. The acute condition should resolve before therapeutic carbohydrate restriction is considered.
Common conditions that are compatible with carbohydrate restriction
Other conditions, as detailed below, are much more common and do not preclude the use of carbohydrate restriction.
1. History of gout/hyperuricemia
Can patients with a history of gout do a low-carb or keto diet? Yes, definitely, but they may be at increased risk of a gout flare in the first six to eight weeks.3 Therefore, patients with a history of gout may need to pay extra attention to hydration status, and possibly even consider prophylactic medication.4
Over the long term, uric acid levels tend to decrease on low carb, along with other markers of metabolic syndrome. One study showed uric acid going down significantly after six months on low carb.5 This suggests carbohydrate restriction may decrease the risk of gout. Studies find similar results with bariatric surgery, thereby suggesting that weight loss and improved insulin sensitivity are mechanisms that likely contribute to the decreased risk of gout attacks.6
There is also preliminary evidence that the ketone body beta-hydroxybutyrate (BHB) may directly reduce gout flares, as well as decrease inflammation by inhibiting NLRP3 inflammasome-mediated inflammation.7
Will a low-carb diet precipitate gout in some patients without a history of gout?
While short-term studies show a temporary rise in uric acid during the first few weeks of starting a strict low-carb diet, doctors who regularly treat patients with low-carb diets typically do not notice an increase in gout episodes.8 Any increase in risk during the first few weeks is likely small or moderate, with uric acid soon returning to baseline levels or lower.9
What else can be done to prevent or minimize a gout flare?
Along with medication support, as stated above, doctors can encourage their gout patients to:
- Minimize sugar intake: Gout is strongly related to obesity, type 2 diabetes, and metabolic syndrome, conditions in which hyperinsulinemia and insulin resistance are known to contribute to elevated uric acid levels. Therefore, it stands to reason that high consumption of sugar and refined carbohydrates, which can lead to higher insulin levels, would contribute to this underlying cause of gout.10
- Reduce alcohol consumption: Beer and other high-carb alcoholic beverages are of particular concern, but all alcohol consumption should likely be minimized in patients with a history of gout.11
- Drink water with lime or lemon: Adding one to two tablespoons of unsweetened lime or lemon juice to water may minimize risk of a gout flare. This can be done throughout the day in the first six to eight weeks of a low-carb diet. One small pilot study showed citric acid can neutralize uric acid and may reduce uric acid levels.12
2. History of gallbladder issues
Traditional medical advice often maintains that a diet high in fatty foods can predispose patients to the formation of gallstones, gallbladder attacks, and even the eventual need to remove the gallbladder.
Does this mean patients with a history of gallstones or gallbladder removal (cholecystectomy) cannot eat a low-carb, higher-fat diet? No, not at all.
In fact, evidence is mounting that a diet low in fat and high in carbohydrates may increase the risk of gallstones.13 The likely explanation for this relationship is that a low-fat diet causes bile to sit idle in the gallbladder – triggering the creation of stones – rather than being released at regular intervals for dietary fat digestion.14 After stones are formed, when a higher-fat food is then consumed and bile is released from the gallbladder, the stones can get stuck in the bile duct. This typically causes extreme pain in the top-right portion of the abdomen, radiating to the back. Several studies have confirmed the link between weight loss on low-fat diets and gallstones.15
What doctors need to know
The following advice may help your patients with gallbladder issues on a low-carb diet:
- Asymptomatic patients: If stones have been visualized or confirmed but the patient has no symptoms, there is usually no need to do anything. These stones may never become a clinical issue.16
- Symptomatic patients: If patients experience severe pain after eating low-carb or keto meals, they may need to reduce their fat intake or break it into smaller portions throughout the day. In theory, coconut oil and MCT oil may help as they are more readily absorbed, and they do not seem to require pancreatic lipase or stimulate bile release.17 However, the benefit of changing dietary oils is mostly anecdotal, without clear consensus; additionally, it would be cumbersome to replace all oils with MCT or coconut oil. Nonetheless, it may be worth trying all these interventions prior to recommending drugs or elective surgery.
- Patients without a gallbladder: A low-carb diet can be consumed when the gallbladder has already been removed, but patients may need to eat smaller, more frequent meals with smaller amounts of fat at any one time, at least in the beginning.18 The liver still makes bile to dissolve the fat, but the gallbladder can no longer concentrate and store it. Instead, bile is released directly into the intestine. Consuming high-fiber, low-carb foods with meals, such as above-ground vegetables or keto bread, may help slow the digestion of fat and reduce diarrhea.19
There is some evidence that ursodiol, a gallstone dissolving agent, can help patients with post-cholecystectomy pain.20
Will a low-carb or keto diet improve or dissolve gallstones?
No formal study has yet tested these diets on people with gallstones.
However, anecdotally, many people report having their gallstone symptoms eventually disappear on a low-carb diet, sometimes after an initial gallstone attack.21
3. History of kidney stones or kidney disease
Although the evidence is inconclusive, high sodium and animal protein intake are thought to be associated with increased risk of kidney stones.22 Because some, but not all, people starting a low-carb or keto diet may need to increase their salt intake to reduce the symptoms of induction or keto flu, this may raise concerns about the development of kidney stones.23 However, as far as we know, research to date has not found that kidney stones occur more often among those who follow a low-carb or ketogenic diet.24
Instead, most reports of kidney stones are anecdotal from adults who develop a kidney stone soon after starting a low-carb diet. However, since kidney stones are very common — occurring in 10% of men and 7% of women in the US, the majority of whom eat a standard American diet — the timing of a stone forming might have nothing to do with beginning a low-carb diet.
If kidney stones do form while following a low-carb diet, make sure your patient stays well-hydrated and avoids large amounts of high-oxalate foods such as chocolate, spinach, okra, Swiss chard, and rhubarb. Coffee also contains oxalate but the intake of caffeine is not related to increased risk for kidney stones.25
Regarding kidney dysfunction, studies have shown no significant risk with moderate- or high-protein intake in the absence of pre-existing kidney disease.26 In fact, low-protein diets may benefit those with advanced kidney disease by reducing uremia-induced symptoms, as opposed to slowing the decline in the glomerular filtration rate.27 Therefore, low-carb diets, even those with high protein intake, are likely safe for all except those with advanced kidney disease.
For more details, see our evidence-based guide, What you need to know about a low-carb diet and your kidneys.
4. History of bariatric surgery
Increasingly, more patients are coming to low-carb diets after having had bariatric surgery. A low-carb or keto diet can be a valuable addition to sustain permanent weight loss and diabetes remission.28
Avoidance of sugary and starchy foods and adherence to a strict low-carb or ketogenic diet may eliminate the strong cravings, feelings of sugar addiction, and compulsion for binge eating that sometimes underlie patients’ past struggles with obesity.29
Increasingly, evidence shows that sugar can have many addictive qualities, including causing the release of endorphins and providing pleasure and significant, but often dysfunctional, emotional regulation.30 Research also shows a strong risk for addiction transference from food to other substances and behaviors – such as alcohol and gambling – in patients after bariatric surgery, a phenomenon that may be related to the addictive qualities of sugary foods.31
In addition to following a low-carb or ketogenic diet for long-term success, bariatric surgery patients may require their doctor’s help in addressing emotional triggers for eating. This may include helping patients deal with feelings of anxiety, stress, depression, anger, fear, pleasure, boredom, and other uncomfortable emotions that they may have tried to cope with by eating sugary, starchy foods.
5. History of high LDL or statin use
How should you approach a patient with elevated low-density lipoprotein (LDL) cholesterol? The first important concept to understand is that low-carb and keto diets do not raise LDL cholesterol in the majority of individuals. Studies show no overall net increase in LDL in most people, and some studies show a slight decline.32 Although LDL does increase in some people, they are in the minority. In fact, most people see a net improvement in cardiovascular health markers with low-carb nutrition, as it can naturally increase high-density lipoprotein (HDL) cholesterol, decrease triglycerides, and improve the size and density of LDL particles.33
You can read more about evaluating cholesterol within the context of a low-carb diet in our guide, “Low-carb cholesterol basics.”
If someone has an increase in LDL after starting low carb, then we recommend putting that into perspective along with their overall cardiovascular risk. Improved blood glucose, blood pressure, weight, and other health parameters may or may not mitigate the impact of increased LDL. For instance, one study showed an improved overall 10-year cardiovascular risk estimation despite an increase in LDL.34
In short, elevated LDL should not be a contraindication to low carb, but rather an opportunity to assess and address overall cardiovascular risk. However, significant elevations of LDL after starting a low-carb diet – even in the setting of overall improved metabolic health – may necessitate a change in diet and/or the addition of cholesterol-lowering medication. We simply do not have evidence to prove that very-high LDL isn’t dangerous in the aforementioned situation, and individualization of care is needed.
What if your patient is already taking a statin? Should that affect your decision to prescribe a low-carb diet? Definitely not. In fact, many doctors see a statin combined with a low-carb diet as an effective way to treat patients at high risk for heart disease, given that the combination can improve diabetes, metabolic disease, obesity, and lower LDL all at the same time.35
The overall benefit may lower your patient’s risk enough that a statin is no longer warranted based on 10-year cardiovascular risk scores. Although we do not have studies to evaluate stopping statins in this setting, it is an intriguing question to address if the patient’s risk drops below the 5% 10-year risk estimation.
As with any medication, continuing or stopping it requires a detailed evaluation of the potential risks and benefits, sometimes including additional testing to assess cardiovascular risk. For instance, current guidelines recommend a coronary calcium score be taken into consideration when statin use is considered for those at intermediate risk of heart disease. This is because evidence suggests there is limited benefit from statins with a coronary calcium score of less than 100.36
In conclusion, elevated LDL and/or use of a statin is still compatible with starting, and benefiting from, carbohydrate restriction.
These Diet Doctor guides may help you and your patient re-frame the risk-benefit analysis:
Patients with pre-existing health issues - the evidence
This guide is written by Dr. Evelyne Bourdua-Roy, MD and was last updated on October 3, 2022. It was medically reviewed by Dr. Michael Tamber, MD on October 19, 2021 and Dr. Bret Scher, MD on October 3, 2022.
The guide contains scientific references. You can find these in the notes throughout the text, and click the links to read the peer-reviewed scientific papers. When appropriate we include a grading of the strength of the evidence, with a link to our policy on this. Our evidence-based guides are updated at least once per year to reflect and reference the latest science on the topic.
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American Journal of Kidney Disease 1996: Effects of dietary protein restriction on the progression of advanced renal disease in the Modification of Diet in Renal Disease Study [randomized trial; moderate evidence] ↩
Although we are not aware of any studies examining ketogenic diets in these populations, it makes mechanistic sense that it would likely not be safe to try a low-carb, high-fat diet. ↩
This is based on findings that uric acid levels may rise initially on a low-carb diet. However, clinical experience shows that the increased risk of a gout flare is small, if it exists at all. [weak evidence] ↩
Medications should only be started after consulting with one’s medical provider.
Some recommend that people who’ve previously had troublesome gout attacks may want to consider using the drug allopurinol while starting low carb.
However, rheumatologist Dr. Edward Skol from Scripps Clinic warns against empirically starting allopurinol, as it’s known to initially increase the risk of an acute attack when given alone. This is supported by the American College of Rheumatology official guidelines, which instead recommend taking a medication like colchicine or ibuprofen if needed.
But, as Dr. Skol summarizes, “The best advice is probably just avoiding dehydration when starting a ketogenic diet.”
Annals of Rheumatic Diseases 2017: Weight loss for overweight and obese individuals with gout: a systematic review of longitudinal studies [review of observational and randomized studies, weak evidence]
Other human studies show an increase in insulin levels causes a reduction in the excretion of uric acid. This suggests that hyperinsulinemia and insulin resistance cause retention of uric acid, increasing the risk of a gout attack.
American Journal of Physiology and Renal Physiology 2017: Insulin stimulates uric acid reabsorption via regulating urate transporter 1 and ATP-binding cassette subfamily G member 2 [mechanistic study in rats article; ungraded]
An initial increased risk of gout attacks is also seen after acute rapid weight loss following bariatric surgery.
Sugar may be worse than other carbohydrates because it is 50 percent fructose, which raises uric acid levels. This study showed lowering the glycemic index of carbohydrate foods improved uric acid levels:
Fructose consumption is strongly linked to uric acid levels:
Moreover, the prevalence of gout correlates with the amount of sugar consumption in populations, as demonstrated by the rise in incidence of gout in 18th century Britain, when sugar consumption rose dramatically:
This study showed most types of alcohol, even in moderate amounts, increased risk of gout. However, it is likely that none of the participants were on a low-carb diet:
However, in one large trial, there was no positive association between the consumption of wine and the incidence of gout, which was in contrast to other alcohol-containing beverages.
In addition, consumption of citrate has been shown to further reduce serum uric acid:
Endocrine Research 2010: The alkalizer citrate reduces serum uric acid levels and improves renal function in hyperuricemic patients treated with the xanthine oxidase inhibitor allopurinol [randomized trial; moderate evidence]↩
International Journal of Obesity and Related Metabolic Disorders 1988: Gallbladder motility and gallstone formation in obese patients following very low calorie diets. Use it (fat) to lose it (well) [non-randomized trial; weak evidence] ↩
Most surgeons agree with this, although some maintain the idea that laparoscopic surgery is such a risk-free procedure in most patients that it benefits the long-term prognosis in asymptomatic cholelithiasis.
Digestive Disease Science 2007: Asymptomatic cholelithiasis: is cholecystectomy really needed? A critical reappraisal 15 years after the introduction of laparoscopic cholecystectomy [overview article; ungraded] ↩
This is based on the clinical experience of practitioners who use low-carb diets and was unanimously agreed upon by our low-carb expert panel. You can learn more about our panel here [weak evidence]. ↩
A low-fat diet is traditionally recommended after cholecystectomy, but scientific proof for this is lacking. In this study, there was no correlation between postoperative problems and fat intake:
Increased sodium intake is linked with calciuresis which could increase stone formation.
In addition, increasing calcium in the diet can decrease urinary oxalate, thus potentially decreasing stone risk.
Nephrology, Dialysis and Transplantation 1998: High-calcium intake abolishes hyperoxaluria and reduces urinary crystallization during a 20-fold normal oxalate load in humans [observational study, weak evidence]
Kidney stones have been reported in children with epilepsy who use special, highly-restrictive versions of ketogenic diets, but supplementing with potassium citrate may reduce the risk of kidney stones five-fold:
Importantly, this doesn’t seem to be a concern with less-restrictive, low-carb diets that consist of whole foods, based on numerous published studies – none of which has shown an increased incidence. See the full list of studies in our guide The science of low-carb and keto. ↩
In fact, increased caffeine has an inverse relationship to kidney stones in some population-based observational studies.
World Journal of Urology 2020: Tea and coffee consumption and pathophysiology related to kidney stone formation: a systematic review [review of randomized and nonrandomized studies, weak evidence]
Journal of the American Dietetic Association 2010: Renal function following long-term weight loss in individuals with abdominal obesity on a very-low-carbohydrate diet vs high-carbohydrate diet [randomized trial; moderate evidence]
While the question of how to define reversal and remission of type 2 diabetes has not been settled, researchers at Virta Health and at the American Diabetes Association have developed a working definition.
Virta defines diabetes reversal as: HbA1c below 6.5% without medications, except metformin. Diabetes partial remission: At least a 1-year duration with HbA1c level between 5.7-6.5%, without any medications (two HbA1c measurements). Diabetes complete remission: Normoglycemia of at least 1-year duration, HbA1c below 5.7%, without any medications (two HbA1c measurements)
According to the ADA:
Partial remission is an A1C <6.5%, fasting glucose 100–125 mg/dl (5.6–6.9 mmol/l) of at least 1 year’s duration in the absence of active pharmacologic therapy or ongoing procedures.
Complete remission is a return to “normal” measures of glucose metabolism, A1C in the normal range, fasting glucose <100 mg/dl (5.6 mmol/l) of at least 1 year’s duration in the absence of active pharmacologic therapy or ongoing procedures. ↩
Journal of Genetic Syndromes and Gene Therapy 2011: Neuro-genetics of reward deficiency syndrome (RDS) as the root cause of “addiction transfer”: A new phenomenon common after bariatric surgery [overview article; ungraded] ↩
Obesity Reviews 2012: Systematic review and meta‐analysis of clinical trials of the effects of low carbohydrate diets on cardiovascular risk factors [systematic review of randomized trials; strong evidence]
Cardiovascular Diabetology 2018: Cardiovascular disease risk factor responses to a type 2 diabetes care model including nutritional ketosis induced by sustained carbohydrate restriction at 1 year: an open label, non-randomized, controlled study [non-controlled study; weak evidence] ↩
Cardiovascular Diabetology 2018: Cardiovascular disease risk factor responses to a type 2 diabetes care model including nutritional ketosis induced by sustained carbohydrate restriction at 1 year: an open label, non-randomized, controlled study. [non-randomized trial; weak evidence]
Nutrition Reviews: Effects of carbohydrate-restricted diets on low-density lipoprotein cholesterol levels in overweight and obese adults: a systematic review and meta-analysis [systematic review of randomized trials; strong evidence]
British Journal of Nutrition: 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] ↩
Cardiovascular Diabetology 2018: Cardiovascular disease risk factor responses to a type 2 diabetes care model including nutritional ketosis induced by sustained carbohydrate restriction at 1 year: an open label, non-randomized, controlled study. [nonrandomized trial, weak evidence] ↩
Diabetologia 2012: In type 2 diabetes, randomisation to advice to follow a low-carbohydrate diet transiently improves glycaemic control compared with advice to follow a low-fat diet producing a similar weight loss [randomized trial; moderate evidence]