The point of keto is to force your body to deplete its glucose (and the stored form, glycogen) so it will have to use body fat as a fuel source. It’s capable of making ketone bodies from your fat, which can replace glucose as an energy-storing molecule if necessary. To do that, you have to break apart fat molecules thus ‘burning’ the fat off. But here’s the thing: your body really really doesn’t want to run out of glucose. No glucose means starvation as far as it’s concerned—even if you're not feeling hungry, your body is still missing one of its key macronutrients. And when you’re (nutritionally) starving, your body will start to break down protein just to get those sweet, sweet carbs. Of course, you have a source of protein in your body already: your own muscles. “When in starvation mode, your body breaks down muscle in your body,” says Giancoli. “Ketosis is a way of trying to preserve that protein. It’s not ideal, but it’s your body’s way of saving you.”
This is why epilepsy patients have to get prescribed diets from profession nutritionists. Without getting into true ketosis, dieters risk ingesting an enormous amount of fat—and potentially a lot of saturated fat, if you’re eating animal meat—without any of the fat-burning effects of ketosis. "The fat is the thing that's problematic for a lot of people on keto," Fung says. "They basically give a pass for any types of fat and a lot of the recipes encourage saturated fats like butter." Dieters who are careful to focus on healthy, unsaturated fats like those in avocados may not have issues, but again Fung notes that you end up with a fairly monotonous diet that way, and thus a lot of people end up eating more saturated fats. "To me as a nutritionist, that's pretty scary."
Some research suggests that ketogenic diets might help lower your risk of heart disease. Other studies show specific very-low-carb diets help people with metabolic syndrome, insulin resistance, and type 2 diabetes. Researchers are also studying the effects of these diets on acne, cancer, polycystic ovary syndrome (PCOS), and nervous system diseases like Alzheimer's, Parkinson's, and Lou Gehrig's disease.
Longer-term ketosis may result from fasting or staying on a low-carbohydrate diet (ketogenic diet), and deliberately induced ketosis serves as a medical intervention for various conditions, such as intractable epilepsy, and the various types of diabetes. In glycolysis, higher levels of insulin promote storage of body fat and block release of fat from adipose tissues, while in ketosis, fat reserves are readily released and consumed. For this reason, ketosis is sometimes referred to as the body's "fat burning" mode.
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If you’re looking to get a jump start on your health and fitness goals this year, you may be thinking about trying the ketogenic diet. Maybe you’ve heard the phrase before — it’s a huge diet buzzword — but aren’t sure what it means. Here’s a primer: The ketogenic diet is an eating plan that drives your body into ketosis, a state where the body uses fat as a primary fuel source (instead of carbohydrates), says Stacey Mattinson, RDN, who is based in Austin, Texas.