Research shows little benefit to ketogenic diet

  • Published
  • By Guy Leahy and Kirsten David
  • Health Promotions Program

Over the past few years, high-fat, low-carbohydrate ketogenic diets have become very trendy and popular.

Advocates of ketogenic diets claim these diets result in greater weight loss, plus reductions in heart disease, diabetes and cancer risk factors over more traditional diets. In addition, ketogenic diets have been claimed to improve endurance performance in comparison to diets with more carbohydrates.

What is a ketogenic diet, anyway? Ketogenic diets contain very low amounts (5-10 percent) of calories from carbs, 25 percent of calories from protein and 70 percent of calories from fat. This is in contrast to more traditional diets, which recommend 45-65 percent carbs, 10-35 percent protein and 20-35 percent fat.

The popular idea behind ketogenic diets is that high-carb diets increase production of the hormone insulin; insulin makes people fat and obesity is linked to heart disease, high blood pressure and diabetes. By eating very few carbs, the ketogenic diet is supposed to force the body to burn fat as fuel, thereby producing weight loss and reducing the risk of these diseases.

Do these claims have any scientific support?

For example, those who support ketogenic diets will point out that 100 years ago, heart disease was not the No. 1 cause of death, as it is now. They indict our modern, high-carb diet for the high heart-disease death rates seen today.

The primary cause of death in 1900 was not heart disease, but infectious disease such as flu or pneumonia, tuberculosis and gastrointestinal infections. Plus, the average life expectancy in the U.S. in 1900 was 47 years.

Today, the average life expectancy is 79 years. In 1900, many adults did not live long enough to die from heart disease.

In addition, heart disease is not a “modern” disease; CT scans of 3,500-year-old Egyptian mummies show ancient Egyptians developed heart disease at the same rate and severity as modern Egyptians do.

Are ketogenic diets effective for weight loss? When compared to a low-fat diet, subjects on ketogenic diets do lose more weight for the first six months, but at the one-year mark, the amount of weight lost is not different.

The effects on cardiovascular risk factors, such as cholesterol, blood pressure and blood sugar, are inconsistent when compared to low-fat diets. A few ketogenic diet studies do show greater improvements some heart-disease risk factors than with low-fat diets; this is probably due to the greater weight loss seen in short-term studies, not the carb content of the diets.

No long-term studies of ketogenic diets in adults without weight loss exist, but some long-term studies of children treated with ketogenic diets for epilepsy suggest these diets may have negative impacts on cardiovascular health. One recent study found that a ketogenic diet was no better than a high-carb diet for weight loss, but that the ketogenic diet resulted a greater loss of muscle mass than the high-carb diet.

Another new study found that low-fat, rather than low-carb, diets may be better for fat loss.

Another benefit claimed by advocates of ketogenic diets is that such diets can improve sports performance. The theory behind this is that by increasing the body’s fat-burning capacity, this would conserve carbohydrate stored in the body, which would prolong the ability to exercise at a higher intensity for a longer period of time.

Many studies have looked at whether ketogenic diets benefit athletic performance, and the answer appears to be “no.” The research on this has consistently shown ketogenic diets do not enhance performance in endurance events.

In fact, it seems such diets actually impair, not enhance, performance. The reason for this is that when the body’s fat-burning engine revs up, the body’s carb-burning engine gears down.

Since carbohydrates are a much more efficient fuel than fat, athletic performance is compromised when carbs cannot be used as a source of energy. Further evidence of the importance of carbs for endurance events is new data that shows carbs are the primary source of fuel for running and cycling competitions up to two hours in length.

There’s simply no way the body can burn fat as efficiently as carbs; the chemistry to do so doesn’t exist. A recent scientific review concluded: “The current interest in low-carbohydrate, high-fat diets for sports performance is based on enthusiastic claims and testimonials rather than a strong evidence base.”

In conclusion, though ketogenic diets are very popular, there is no convincing scientific evidence these diets produce greater body-fat loss or improve health beyond more traditional diets, such as the Mediterranean diet. There is also no evidence ketogenic diets result in superior athletic performance.

Be skeptical of advice from “experts” who lack professional training in nutrition and dietetics. The best way to determine what your meal plan should look like is to consult someone who has a degree in the field, and who is a registered dietitian or sports dietitian.