The keto diet has a massive fan base that has grown at least in part due to the popular Netflix documentary The Magic Pill, which touts a trove of promising keto health benefits. But the fact of the matter is that most of the studies on the keto diet are premature. Meaning: They’re in small populations of humans, or they’re in rats. (And you are very different from a rat.)

All of our cells need fuel to function. This fuel comes from three sources: fat, carbohydrates and protein, called macronutrients. Too much protein without fat puts us at risk for a handful of complications, so protein can never healthily serve as a primary source of fuel. We are left then with fat and carbohydrates as the main providers of energy – the energy that allow us to do everything from breathing and blinking as we veg out on the couch to swimming the English Channel. Our cells’ preferred fuel comes from carbohydrates, which are easily converted to glucose, which, in turn, is readily converted to energy. This is why athletes “carb load” before they compete. Peak performance occurs when the body has plenty of glucose and glycogen stores available at hand. When glycogen runs out, that’s when the body turns to fat. When there is no more blood sugar for our cells to consume, they seek an alternative form of energy. This energy comes from ketones, which are compounds our body produces from stored fat. So a ketogenic diet is one that is high in fat and very low in carbohydrates, resulting in the production of ketones to be used for fuel instead of glucose.

The keto diet is a low-carb, high-fat dietary regimen which has been linked to improvements in insulin sensitivity and higher rates of weight loss — both positive factors in managing type 2 diabetes. Lowering carb intake induces a metabolic state known as ketosis, through which the body produces ketones which burn fat — rather than carbohydrates — for energy.
When a person goes off the ketogenic diet and regains much of their original weight, it’s often not in the same proportions, says Kizer: Instead of regaining lean muscle, you’re likely to regain fat. “Now you’re back to your starting weight, but you no longer have the muscle mass to burn the calories that you did before,” she says. “That can have lasting effects on your resting metabolic rate, and on your weight long-term.”
Beyond the short-term effects of the keto flu, the diet can also negatively impact your digestion and gut in the long run. One 10-year study conducted on using keto to manage pediatric epilepsy found the following GI side effects over time: constipation, high triglyceride levels, high cholesterol, diarrhea, lethargy, iron deficiency, vomiting, and kidney stones.
The research on how diet affects PCOS is minimal, but there is one compelling study on the ketogenic diet and women with PCOS. In this study, five overweight women ate a ketogenic diet (20 grams of carbohydrates or less per day) for 24 weeks. The results were astounding — average weight loss was 12%, free testosterone decreased by 22%, and fasting insulin levels dropped by 54%. What’s even more impressive is that two of the women became pregnant despite previous infertility problems.
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