Shahar Madjar, MD

Dieting is a sensitive topic. People become emotional, defensive, even tribal. Yes! Dieters divide themselves into tribes: The Vegans; The Ketos; The Paleos; The Calorie-Counters; The Meal-preparers; The Mediterraneans. In my last article, I described some of the beneficial effects of ketogenic diets (low-carb, high-fat diets). I wrote that a ketogenic diet can lead to impressive short-term weight loss. It can also improve HDL (good cholesterol), decrease triglyceride levels, and significantly improve, even cure diabetes. And I asked: are keto diets effective in the long run? And what are the short-term side effects and the long-term consequences of staying on such a diet? Today, I will tell you more about keto diets. If you belong to the keto tribe, please don’t take what I write here personally. I am just trying to present the most updated version of scientific evidence.

When talking about keto diet, any diet, the question isn’t only if a certain diet would lead to weight loss, but if it is better than any other diet. Since the amount of protein needed to maintain good health is relatively constant, the main difference between diets would be in the consumption of carbs vs fats. Several meta-analyses (studies that analyze and summarize the results of several prior studies) have shown that in the short run, low-carb diets may result in greater weight loss than low-fat diets. But studies that spanned for longer than 6 months suggest that low-carb diets and low-fat diet are equivalent in their effects on weight loss.

In addition, the side effects of keto diets are considerable. Their severity is dependent on the degree of carb restriction. In the short term, dieters may experience gastrointestinal symptoms such as constipation, nausea, and abdominal pain. These may last for several weeks. Some dieters will experience flu-like symptoms such as lightheadedness, dizziness, fatigue, even poor sleep. Others may experience headaches, skin rash, diarrhea, dehydration, hypoglycemia (decrease in blood glucose level), hyponatremia (reduced blood sodium). Some keto dieters experience keto-breath, or metallic taste in their mouth. Friends and loved ones may notice fruity-smelling breath, or a whiff of nail-polish remover. In short, butter and bacon may not be as fun as advertised.

At special risk of complications are individuals with a history of heart disease, atrial fibrillation, and heart failure, those diagnosed with kidney or liver disease, and anyone with significant medical conditions. These individuals should consult a capable physician prior to embarking on a keto diet.

Perhaps the most concerning is the possible association between low-carb diets and mortality. In an April 2019 article in the European Heart Journal, Mohsen Mazidi and his colleagues examined the link between low-carb diets and death. They used data that was collected between 1999 and 2010 by the US National Health and Nutrition Examination Survey. The 24,825 participants in the study were asked to recall their food consumption during the two days before their interview. They were asked questions regarding the type and quantity of the foods and beverages they consumed. Their answers were analyzed. Each participant was then assigned a score depending on their relative consumption of proteins, carbs, and fats. The participants were then divided into four groups according to their carb consumption.

The results were dramatic! Participants who consumed the least amount of carbs had the highest risk of overall mortality (32% higher chance of death). They also had higher risks of mortality from heart disease and strokes, and even from cancer. The researchers then analyzed the results of 9 other studies with a total of 462,934 participants. Here, too, there was a link between low-carb diets and overall mortality. Low-carb diets were also associated with mortality from heart disease, and mortality from cancer.

These results should be interpreted with caution. These are observational studies. Participants were not randomly assigned into different diets and were not monitored on a continuous basis. The information about their diets was collected only once. They were asked to recall, rather than to record their foods and beverages. What if they didn’t recall correctly? What if their food consumption on those days didn’t represent their typical diets? What if there are other factors that weren’t captured in the analysis? Besides, perhaps the keto diet–an extreme case of low-carb diet–is inherently different from other low-carb diets?

Here is my take: The research linking low-carb diets with mortality doesn’t necessarily imply a cause-and-effect relationship. In other words, we can’t say for sure that low-fat diets, or keto diets, cause earlier death. But the association is there, it is something to consider, it is disturbing. And why, of all diets, would one chose a diet with such a history?