Many people are attracted to low-carb diets because they hear that it can help them lose weight and improve their health. But the reality is that so many people — and doctors — struggle to find a scientifically-valid reason to go low-carb. Unfortunately, that means that the vast majority of people can’t do it correctly, and they end up losing their weight instead of gaining it.
When a friend asks me for advice on low carb diets, I always ask for their goals. Do they want to lose weight? Do they want to improve their health? Or perhaps improve their athletic performance? If their goals are strictly weight loss, then I will advise them to eat carbs at every meal to keep their metabolism stoked. However, if their goal is to improve their health, I’ll recommend instead that they avoid refined carbohydrate foods like white rice and stick to whole grains. This may not be the best diet for weight loss, but it is the best diet for health.
From , medical opinion from – Updated 24. June 2023
The low-carb, high-fat (LCHF) diet enjoyed a resurgence in popularity in 2018, with the ketogenic diet becoming the most Googled diet of the year, and it retains that honor in 2019. You have probably heard this more than once, including from patients.
The low-carb diet is not new, of course. The complete foods that make up a low-carb diet are similar to what people have been eating for thousands of years. However, the popularity of low-carb diets has recently been accompanied by new scientific evidence on their health benefits.
Scientific studies of varying quality and duration show that low-carb diets (typically less than 100 grams of carbohydrates per day) and ketogenic diets (less than 20-30 grams of carbohydrates per day) have many health benefits, including:
As popular as they are, and despite the many health benefits demonstrated in the scientific literature, many people unfortunately still consider low-carb and ketogenic diets to be categorically harmful and dangerous.
Why is there such a disconnect? The answer may lie in a lack of understanding of the science behind low-carb diets.
This guide explains the scientific facts and addresses the misconceptions about low-carb diets. If you are a physician, we hope this guide will help you examine the risk-benefit ratio of low-carb diets.
If you are not a health care professional, this guide can help you prepare for the most common problems that health care professionals face. Your own experience with a low-carb diet, along with this guide, will help your doctor better understand the potential benefits of a low-carb diet.
Below are some science-based explanations to help you distinguish fact from fiction:
Deception 1: Dietary ketosis is identical to ketoacidosis
Doctors probably never learned about nutritional ketosis in medical school or during their fellowship. Instead, ketones are usually only mentioned in the context of a potentially fatal condition called ketoacidosis.
Ketoacidosis occurs mainly in people with type 1 diabetes and is the result of insulin deficiency and a sharp rise in blood sugar levels. Under these conditions, ketone levels rise to more than 7 mmol/l (and usually to more than 10), making the blood more acidic and putting the person at high risk.
However, ketoacidosis is very different from nutritional ketosis, in which ketone concentrations in the blood are usually between 0.5 and 4 mmol/L and are accompanied by adequate insulin levels and low blood glucose. However, nutritional ketosis and ketoacidosis are physiologically very different, and the former form poses virtually no health risk. This basic physiological distinction is important for any healthcare professional to understand.
Concerns about ketosis should not stop doctors from recommending a low-carbohydrate or ketogenic lifestyle.
Deception 2: Low-carbohydrate diets may lead to short-term weight loss, but at the cost of increased risk of heart disease or death.
With the growing popularity of low-carb diets, there has paradoxically been an increase in studies claiming that these diets increase the risk of premature death or heart disease. Although these studies make headlines, closer examination reveals that they do not contain significant findings and are not related to a well-designed low-carb diet.
For example, in 2013, a review of 17 studies claimed that the risk of death was higher in people who ate fewer carbohydrates. How was the term low-carb defined in these studies? This is a good question because definitions vary from study to study. In most studies, a low-carb diet has been estimated based on the percentage of total calories that are carbohydrates. They did not use the absolute amount of carbohydrate intake as low-carbohydrate therapeutic diets are usually defined.
In general, the lowest carbohydrate intake in these studies averaged about 40% of calories. On a 2000 calorie diet, 40% is 200 grams of carbohydrates. While this is less than the standard American diet (250-400 grams of carbs), it is well above the 20-50 grams of carbs per day of the low-carb and ketogenic diets used to treat obesity and chronic disease.
In addition, most of the studies reviewed did not have quality control for carbohydrates. If a person eats 200 grams of carbohydrates a day, there is a lot of room for refined and processed carbohydrate-rich foods. In a low-carb diet, calories come almost exclusively from vegetables and nuts and not from sweet, starchy, processed foods. Few of the above studies controlled for carbohydrate quality, so the results are unlikely to apply to well-designed low-carb or ketogenic diets.
These observational studies also suffer from healthy user bias. In the 1980s and 1990s, we were told by public health that we should avoid fat and eat more carbohydrates. People in these studies who consumed 40% carbohydrate and 40% fat – that is, who did not adhere to the dietary recommendations for that day – were also more likely to ignore other public health messages, smoke, not exercise and consume more calories. An observational study cannot account for all of these confounding variables, making the data much less useful.
Finally, observational studies can only make assumptions; they cannot demonstrate causal relationships. They may indicate the need for further qualitative studies to assess a possible association, but the low hazard ratios (less than 2.0) found in these studies are likely the result of statistical noise rather than a true association.
In summary, there are no moderate to high quality studies showing that a whole grain, low carbohydrate diet leads to an increased risk of heart disease or premature death.
Deception 3: The allowed amount of fat in a low-carb diet increases LDL cholesterol
It turns out that this is not the case for the vast majority of people who follow a low-carb diet. Most studies show no significant change in low-density-lipoprotein (LDL) cholesterol levels, but do show a possible beneficial effect of increasing HDL levels, lowering triglyceride levels, and reducing small, dense atherogenic LDL particles. In fact, a study calculating participants’ 10-year risk of atherosclerotic cardiovascular disease (ASCVD) found that overall cardiovascular risk decreased with a low-carbohydrate diet.
There is a small group of people, called hyperresponders, in whom the LCHF diet significantly increases LDL levels. The exact size of this population is not known, but it is thought to be 5-25% of those on a low-carb diet.
Although we do not have data on outcomes in this particular population, we must ask whether the increase in LDL levels in a very low-carbohydrate diet is a unique mechanism that may have different consequences than the increase in LDL levels in people on a low-fat diet or a more standard Western diet.
Although studies have shown an association with increased risk in the latter situation, the increased risk for those with a low-carbohydrate lifestyle has not been studied. What is unique about the increase in LDL in a low-carbohydrate diet is that it is almost always accompanied by a decrease in low-density LDL, an improvement in insulin resistance, a decrease in blood pressure, an increase in HDL and a decrease in triglyceride levels.
This begs the question: If a person responds well to a low-carbohydrate diet, do elevated LDL levels have compelling pathological significance when other cumulative beneficial effects are present?
Although the answer to this question is not exhaustive, it is important to consider the patient’s cardiovascular risk as a whole and interpret any lipid changes in the context of the individual’s overall health profile. This does not mean that LDL should be ignored. Rather, LDL should be considered in the broader context of overall health changes.
In summary, LDL cholesterol levels are not elevated in most people following the LCHF diet. For those with elevation, this should be interpreted in the context of possible improvement in other cardiovascular risk factors. Until long-term data is available, these cases should be assessed in detail on an individual basis rather than automatically assuming a net disadvantage or benefit. You can read more in our post about our official position on LDL cholesterol.
Cholesterol and low-carb diets
AdvisorRead more about what cholesterol is, how your body uses it, why low-carb and keto diets can cause changes in blood cholesterol levels, and whether you should be concerned if your cholesterol levels rise with a keto or low-carb lifestyle.
Deception 4: Excessive protein intake in a low-carb diet can lead to kidney damage, osteoporosis, and heart disease.
This persistent myth is false on two counts. First, most low-carb diets contain little protein. Most contain 20-30% of calories from protein, which can be as much as 70-150 grams of protein per day, well within the normal recommended allowance of 10-35% of calories.
There is no evidence that protein intake at these levels is harmful to people with normal or even moderately impaired kidney function. If someone already has severe kidney disease, a moderate protein diet can be potentially dangerous. In this case, a low-carb diet should be used with caution. However, most LCHF and ketogenic diets are probably safe for everyone except people who already have advanced kidney failure.
Moreover, protein consumption does not lead to poor bone health. In fact, insufficient protein intake likely contributes to bone loss. The concern that too much protein makes the blood more acidic and thus damages our bones is a baseless claim unsupported by qualitative evidence, which is described in more detail here.
Finally, protein intake is not correlated with the risk of heart disease. As noted in Fat and Heart Disease, the evidence for a link between protein intake and heart disease comes from weak nutritional epidemiological studies that do not demonstrate a causal relationship. Some studies, such as. B. the Nurses’ Health Study, shows an inverse relationship between protein intake and heart disease risk.
Protein in a low-carb or keto diet
Guide Along with fats and carbohydrates, protein is one of the three macronutrients (macros) in the diet and plays a unique and important role in the body. Here’s a guide to everything you need to know about protein in a low-carb or ketogenic lifestyle.
Deception 5: Meat and fat allowed in low-carb diets increase cancer risk
For a detailed assessment of fat intake and cancer risk, see our guides on Diet and Cancer and Saturated Fat. In short, the evidence on the link between fat and cancer risk is inconsistent, incomplete and unreliable.
Observational studies indicating an increased risk of colorectal cancer due to red meat have many shortcomings common to all studies on the epidemiology of diet-related chronic diseases. It is important to note that a recent series of studies published in the Annals of Internal Medicine shows that the available evidence from randomized controlled trials and observational studies does not support recommendations to limit red meat consumption to prevent cancer and heart disease.
Despite the lack of evidence, the World Health Organization has classified red meat as a probable carcinogen. However, WHO relied almost exclusively on epidemiological studies and included only three randomized controlled trials in humans. This is a very important point because randomized controlled trials, which represent a much larger body of evidence, do not show an association between red meat and cancer risk.
Moreover, the WHO seems to have ignored the results of other observational studies that have found no link between meat and cancer. Thus, the WHO assessment is incomplete from a medical-scientific perspective, and the quality of the evidence does not support the strength of the conclusion. For more on the science behind concerns about red meat and cancer, see our factual guide on red meat.
Moreover, there is no link between fat consumption and breast cancer. The Women’s Health Initiative (WHI), the largest randomized trial on the subject, found no association between increased fat intake and increased risk of breast cancer. Moreover, a meta-analysis of seven prospective studies involving 337,000 women also found no association between fat intake and breast cancer risk.
Overall, the highest quality data do not suggest a causal relationship between fat intake and increased cancer risk.
Nutrition and cancer: What we know and what we do not know
In this guide, we look at what we know about nutrition and cancer – and what we don’t.
Deception 6: Whole grains are an essential part of a healthy diet
First of all, there is no nutritional need for carbohydrates.
We cannot live without essential amino acids and essential fatty acids, but there are no essential carbohydrates. Whole grain cereals are not essential for survival. But are they proven to be good for your health?
Studies show that whole grains are associated with better health than refined grains. This is not surprising, given the lack of nutritional value and potentially harmful health effects of refined grains. However, there are no studies that compare whole grains to a diet without whole grains.
In support of the importance of whole grains, there is also evidence of so-called blue zones, societies where people are much more likely to stay healthy until the age of 90 and 100 than the general population. These communities often have high levels of fiber and whole grains in their diets. However, we must acknowledge that their calorie intake is on average two-thirds lower than that of people in most developed countries, that their food is mostly grown locally and prepared at home, that they do not eat fast food or processed food, that they are physically active throughout their lives, and that they have strong social bonds.
Moreover, these conclusions are not based on any research, but are simply observations of a population whose lives are very different from those of modern industrial societies. The results obtained in these societies cannot be accurately extrapolated to countries where only 12% of the population can be considered metabolically healthy.
As a healthcare provider, determine if your patient has a diet high in refined grains. If so, switching to whole grains is probably beneficial. If not, there is not enough evidence to support the health benefits of whole grains.
For more information, see our full guide on whole grains.
Healthy whole grain products: What the evidence really shows
Guide Do whole grain products live up to their reputation as superfoods? Let’s take a closer look at the very weak scientific evidence behind the claims of their benefits.
Deception 7: Low-carb diets contain no fiber
Low-carb diets generally contain little fiber. In fact, many low-carb and ketogenic diets include virtually unlimited amounts of vegetables off the grid, such as broccoli, spinach, cauliflower, Brussels sprouts, green beans, bell peppers, zucchini and others, all of which are high in fiber.
But even if someone chooses a low-fiber, low-carb diet, there’s no evidence that it’s dangerous. As with whole grains, most of the evidence in favor of fiber comes from a comparison of two different high-fiber and low-fiber diets. A high-carb, low-fiber diet is likely to contain highly processed and refined carbohydrates.
High-fiber, less refined and less processed carbs are definitely better than low-fiber, more processed and more refined carbs. However, there is no evidence that fiber is necessary for health or that adding fiber to a low-carbohydrate diet of whole foods is beneficial.
If the recommendation to eat more fiber leads to replacing unhealthy processed grains and carbohydrates with whole, unprocessed grains, increasing the amount of natural fiber is a step in the right direction. However, if the intent is to add fiber to a low-carb diet, then we are acting outside the existing scientific evidence, with no clear evidence of benefit.
Error 8: Dietary fiber is important for a healthy gut microbiome
It’s true that our microbiome feeds on starch fibers, but we don’t know if it should. For example, our intestinal flora digests starch into butyrate, a short-chain fatty acid. Butyrate is structurally similar to beta-hydroxybutyrate (BHB), the main ketone body produced in dietary ketosis.
Moreover, studies claiming that low-carb diets negatively affect the microflora in the gut suffer from the imprecise definition of a low-carb diet, which includes 40% calories and large amounts of industrial rather than natural fats. Furthermore, since these studies do not account for carbohydrate quality, they cannot be extrapolated to an all-carbohydrate diet. The quality of carbohydrates is probably an important factor, as the health of the microbiome depends on the ratio of good to bad bacteria. Reduction of refined carbohydrates, without further intervention, likely reduces bad bacteria and thus improves the ratio.
Finally, there is no conclusive evidence that changes in the gut microbiome resulting from a low-carbohydrate, high-fat diet have future health implications. Again, the science is clouded by the fact that the subjects ate poor quality food with a high percentage of processed foods.
Scientists are still in their infancy in studying the gut microbiome, and there’s still a lot we don’t know. More important than the microbiome is the influence of diet on a person’s overall health. If a person’s health improves significantly with a low-carbohydrate diet, we have to ask how significant the changes in the microbiome are.
Deception 9: Low-carb diets are too restrictive
This statement is in the eye of the beholder. Finally, doctors can recommend a vegan diet without fear of it being too restrictive, even if it excludes all animal products.
Fancy eating just about any vegetable, meat, cheese, egg, poultry, fish, nut or seed you like? For some, this seems like paradise. Saying it is a restrictive regime is a matter of opinion.
The challenge for practitioners is to find the right approach for each individual. Some find a low-carb diet restrictive, others find a vegan diet restrictive. Either way, it’s not for us to decide.
Deception 10: Too difficult to maintain in the long term
Let’s face it. Any major lifestyle change has a low rate of adherence. Quitting smoking, regular exercise programs and even a vegetarian diet are difficult to control in the long run. However, if an intervention is a healthy approach for the individual, the fear of adherence should not stop us from offering it. Instead, we need to provide enough support to help the person sustain the change.
Despite the difficulty in changing long-term behavior, some studies show excellent adherence to the ketogenic diet. A non-randomized study by Virta Health found that adherence after one and two years was 83% and 74%, respectively. While these data are not representative of the general population, they show that people who choose to follow a low-carb diet can thrive and excel with the right support.
Emphasizing the importance of behavioral changes and improving the logistical support mechanisms for these changes, low-carbohydrate diets could play an important role for many patients.
Deception 11: Physicians should follow recommendations for prescribing lipid- and calorie-reducing diets
The guidelines are changing. Low-carbohydrate diets are now recognized as an official treatment option by the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD). This makes low-carb diets a recognized therapy.
Moreover, there is increasing evidence in peer-reviewed journals that low-carbohydrate diets should be considered evidence-based medicine. Dr David Unwin in the UK has published reports on his success with low-carb diets and has influenced the recommendations of the Royal College of General Practitioners. In addition, Virta Health has published the results of using a ketogenic diet to treat and reverse type 2 diabetes. In contrast, there are no published studies using the standard ADA diet to reverse diabetes, as there are with the low-carb diet.
There is now ample evidence and professional recognition from the ADA to support the use of low-carbohydrate, high-fat diets for the treatment of diabetes. This support can be extrapolated to pre-diabetes, insulin resistance and the metabolic syndrome with the assurance of evidence-based care.
However, health professionals who are still unsure can begin a 6-month trial of the low-carb diet with the patient, during which metabolic health indicators such as waist circumference, blood pressure, HbA1c, HDL, triglycerides, rapid insulin and other biomarkers are carefully monitored. If all of these indicators improve, that should be enough evidence to support the patient’s decision. It comes down to recognizing that the evidence is there and knowing that patient safety and effectiveness can be verified.
Frequently Asked Questions
Do doctors recommend low-carb diets?
Some doctors recommend low-carb diets for weight loss, but there is not enough evidence to support this.
Why doctors say keto diet is bad?
The ketogenic diet is a high-fat, low-carbohydrate diet that has been used for centuries to treat difficult-to-control seizures in children. The diet forces the body to burn fats rather than carbohydrates. The keto diet is not a healthy way of eating and can lead to nutritional deficiencies, kidney stones, bone fractures and increased risk of heart disease.
Why do doctors recommend Keto?
Keto is a low-carb, high-fat diet that helps to control seizures in children with epilepsy. It also has been shown to help with weight loss and improve brain function.
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