The ketogenic (keto) diet is an extremely low-carbohydrate, very high-fat diet that originated as a treatment for pediatric epilepsy. It has gained popularity recently among athletes and as a weight loss diet. Much stricter than an Atkins-style low-carb diet, an adherent to the keto diet consumes fewer than 35 grams of carbohydrates daily—less than seven percent (140 calories) of a standard 2000 calorie diet. Unlike other low carbohydrate diets, it is not high in protein, which is only eaten in moderation.
What Ketosis Is. The emphasis of the diet is forcing the body into what’s called ketosis—a metabolic state where fat is the primary source of fuel, in the form of ketones. Normally, the body uses carbohydrate (glucose) as the preferred energy source. During ketosis, burning stored body fat, a normally inefficient process, is emphasized. Adherents point to this fat-burning mode as the secret to fast and sustained weight loss. It is counter-intuitive to think of eating fat in order to lose fat, but the principal theory of the diet is based on knowledge of physiological principles. It is possible, through extreme carbohydrate restriction, to train our bodies to burn more fat, more efficiently.
How Realistic Is It? Often, those who attempt the keto diet aren’t truly reaching ketosis because the amount of allowable carbohydrate is prohibitively low. All grains, pastas, breads, beans, sugar, sweeteners, starchy vegetables, and nearly all fruit are eliminated (exceptions include avocados and very small amounts of berries). Meats, full-fat dairy, eggs, leafy green vegetables, nuts, seeds, and oils are emphasized. Promoters of the diet recommend a two-day period of fasting to transition into the high-fat way of eating, and warn that energy levels may be low for a short time while the body adjusts to using fat as fuel. This transition time is known as the “keto flu,” where bad breath, dry mouth, increased hunger, and excessive urination are potential side effects. Those making the switch to keto use test strips to measure for ketones in their urine.
Short on Science. Like many trendy diets, there is limited research on the long-term effects. Additionally, adherence to the diet is difficult, as eating out and social situations are impacted by the need for special foods. Utilizing stored body fat as energy can lead to weight loss, though the long-term effects of eating extremely high-fat diets are unknown and go against current chronic disease prevention recommendations that emphasize plant foods that are eliminated here. Radically changing how your body processes energy is a health risk, and side effects could include digestive irregularities, muscle cramps, and nutrient deficiencies. Lastly, weight that was lost may return if carbohydrate consumption returns to normal and other weight loss measures aren’t taken.
—Matt Ruscigno, MPH, RD