Diet fads come and go. The ketogenic diet is an extremely low carb, high fat diet that has been used since the 1920s to treat children with drug-resistant epilepsy. However, it’s currently being touted for weight loss by celebrities such as Halle Berry, Kim Kardashian and Melissa McCarthy.

When carbohydrate intake is limited, the level of glucose — normally the body’s main source of energy — falls, forcing the body to burn fat and to a lesser extent protein for energy. This results in compounds called ketones (such as acetone), which can be used for energy by the body. The end result is a metabolic state called ketosis, which also occurs in starvation, uncontrolled diabetes and alcoholism.

People do lose weight on this diet, but most studies show that weight loss is not significantly greater after a year than with other diets. Diabetics on this diet have an improvement in blood sugars and A1C (a blood marker indicating the average blood sugar over the previous three months). However, there are no long-term studies showing lasting benefits from the keto diet, and there are concerns about adverse health effects. Following are some of the concerns:

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• People on this diet tend to have fatigue, bad breath, bloating, constipation, dizziness, sleep problems, and generally just don’t feel well (sometimes referred to as the “keto flu”).

• The keto diet lacks fiber, because fiber-rich food such as whole grains, legumes and many fruits and vegetables are forbidden. Lack of fiber is the reason constipation occurs, and fiber plays a role in many other aspects of optimal human health.

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• Bad cholesterol (LDL) levels rise on the keto diet, due to the high intake of saturated fat.

• At least some of the initial impressive weight loss sometimes seen with the keto diet is due to water loss associated with the state of ketosis — and adequate water is important for optimal health.

• The keto diet is difficulty to maintain, because it basically eliminates a whole food group (carbs).

• The keto diet is low in health-promoting micronutrients, because whole grains, most fruits and many vegetables are eliminated.

The bottom line is that we should be careful about getting nutritional advice from celebrities. Humans did not evolve to eat an extremely low carb diet. There are much healthier ways to lose weight, with lifestyle changes supported by good science. The Paleo diet will be discussed in next week’s column, and the science behind a plant-based, whole food diet with no salt, sugar or added oil the following week.

Dr. Feinsinger, who retired from Glenwood Medical Associates after 42 years as a family physician, has a nonprofit Center For Prevention and Treatment of Disease Through Nutrition. He is available for free consultations about heart attack prevention and other medical issues. Call 970-379-5718 for an appointment. For questions about his columns, email him at gfeinsinger@comcast.net.