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 precaution, but should not preclude carbohydrate restriction. We highlight the few exceptions to this below.
Conditions incompatible with carbohydrate restriction
Advanced renal disease
Patients with advanced renal disease who are not yet on dialysis need low-protein diets that are largely incompatible with carbohydrate restriction.1It’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 body’s inability to properly handle the products of fat digestion. This likewise usually presents 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 starting a high-fat diet.
Certain acute, unstable conditions
Finally, in some cases, patients with an acute, unstable medical condition — such as acute pancreatitis, active liver failure, acute gout, and others — are not candidates for this dietary intervention. The acute condition should be resolved before therapeutic carbohydrate restriction is considered.
Common conditions compatible with carbohydrate restriction
Other conditions, as detailed below, are much more common and do not preclude the use of carbohydrate restriction.
- History of gout/hyperuricemia
- History of gallbladder issues
- History of kidney stones
- History of bariatric surgery
- History of high LDL or statin use
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 prophylactic treatment with allopurinol during the initial stages of carbohydrate restriction.
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.4 This suggests carbohydrate restriction may decrease the risk of gout. There is also preliminary evidence that the ketone body beta-hydroxybutyrate (BHB) may directly reduce gout flares.5
Will a low-carb diet 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 regularly treating patients with low-carb diets typically do not notice an increase in gout episodes.6 Any increase in risk during the first few weeks is likely small or moderate, with uric acid soon returning to baseline levels or lower.7
Clinical observations from low-carb physicians:8
- Almost all uric acid levels return to normal within six to eight weeks.
- Patients who have a previous history of gout are most at risk for developing a gout attack in the first six to eight weeks of low carb. Adjust medications accordingly, or discuss prophylaxis if necessary.
- Patients who do not have a history of gout will likely not experience it, even if their uric acid levels go quite high.
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, so consumption of sugar and refined carbohydrates may contribute to the underlying cause.9 High blood levels of insulin are correlated with increased uric acid levels, probably due to reduced excretion of uric acid by the kidneys.10 Moreover, gout epidemiology parallels sugar consumption in populations, as demonstrated by the rise in incidence of gout in 18th century Britain, when sugar intake also rose dramatically.11 Fructose consumption is also strongly linked to uric acid levels.12
- Reduce alcohol consumption: Beer and other high-carb alcoholic beverages are of particular concern, but all alcohol consumption should be minimized.13
- 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.14
2. History of gallbladder issues
Traditional medical advice maintains that a diet high in fatty foods can predispose patients to the creation 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, high-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.15 The 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. After stones are formed, when a higher-fat food is then consumed and bile 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 low-fat diets and gallstones.16
What doctors need to know
The following advice may help your patients with gallbladder issues on a low-carb diet:17
- Asymptomatic patients: If stones have been visualized or confirmed but the patient has no symptoms, there is no need to do anything. Their stones may never be an issue.
- 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, they do not require pancreatic lipase, and may not stimulate bile release.18 However, this is mostly anecdotal, without a clear consensus. If these methods do not reduce attacks, the patient may eventually need to have elective surgery or be placed on specific drugs to manage gallstones.
- 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. 19 The liver still makes bile to digest 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. There is also inconsistent anecdotal evidence that a bile supplement can help break down fats and reduce diarrhea or other digestive symptoms.20
Will a low-carb or keto diet improve or dissolve gallstones?
No formal study has yet tested these diets on people with gallstones.
3. History of kidney stones or kidney disease
Although the evidence is uncertain, sodium intake is 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. 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.23
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 are on a standard American diet — the timing of a stone forming might have nothing to do with starting low carb.
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 caffeine, chocolate, spinach, okra, Swiss chard, and rhubarb.
Regarding kidney dysfunction, studies have shown no significant risk with moderate- or high-protein intake in the absence of pre-existing kidney disease.24 Therefore, low-carb diets 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. Of course, it is preferable that patients attempt a trial of the diet before life-altering surgery, as it may obviate the need for surgery completely. However, even after bariatric surgery, a low-carb or keto diet can be a valuable addition to promote permanent weight loss and diabetes reversal.25
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.26
Patients who have had bariatric surgery can safely fast, but they should avoid eating one or two large meals during a time-restricted eating window. They can still limit their eating window, but it may be better for them to graze over a 6-hour restricted time period to avoid potential malabsorption or diarrhea. 27
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.28 Recent studies show a strong risk for addiction transference from food to other substances, such as alcohol and gambling, in patients after bariatric surgery, a phenomenon that may be related to the addictive qualities of sugary foods.29
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 managed 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.30 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 an improve the size and density of LDL particles.31
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 sugars, 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 calculation despite an increase in LDL. 32
In short, elevated LDL should not be a contraindication to low carb, but rather an opportunity to assess and address overall cardiovascular risk.
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, as the combination can improve diabetes, metabolic disease, obesity, and lower LDL all at the same time.33
The overall benefit may lower your patient’s risk enough that a statin is no longer warranted based on 10-year risk scores. Although we do not have studies to evaluate stopping statins in this setting, it is an intriguing question if the patient’s risk drops below the 5% 10-year risk calculation.
As with any medication, continuing or stopping it requires a detailed evaluation of the potential risks and benefits of the medications compared to alternatives. For instance, recent 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 recent evidence suggests there is limited benefit from statins with a coronary calcium score of less than 100.34
In conclusion, elevated LDL or use of a statin is still compatible with starting, and benefiting from, carbohydrate restriction.
This Diet Doctor guide may help you and your patient re-frame the risk-benefit analysis:
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] ↩
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: Arthritis and Rheumatology 2017: Effects of lowering glycemic index of dietary carbohydrate on plasma uric acid: The OmniCarb Randomized Clinical Trial [randomized trial; moderate evidence] ↩
Journal of Clinical and Diagnostic Research 2013: Correlation of the serum insulin and the serum uric acid levels with the glycated haemoglobin levels in the patients of type 2 diabetes mellitus [observational study, weak evidence] ↩
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: American Journal or Medicine 2015: Alcohol quantity and type on risk of recurrent gout attacks: An internet-based case-crossover study [weak 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] ↩
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 risk on a less-restrictive diet based on whole foods based on numerous published studies, none of which have shown an increased incidence. See the full list of studies in our guide The science of low-carb and keto. ↩
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. Reversal is defined as having one HbA1c measurement below 6.5% (7.8 mmol/L or 47.5 mmol/mol) without medications except metformin. Partial remission is having at least two HbA1c measurements between 5.7 and 6.5% (6.5 mmol/L or 38.8 mmol/mol and 7.8 mmol/L or 47.5 mmol/mol) over the course of one year without any medications. Complete remission of diabetes is defined as normoglycemia for at least one year, as indicated by at least two HbA1c measurements below 5.7% (6.5 mmol/L or 38.8 mmol/mol) and no medications. ↩
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] ↩
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] ↩