The ketogenic diet is currently one of the hottest weight-loss plans around. It involves consuming very few carbohydrates—typically 20 grams (about the amount in a small banana) to 50 grams (about the amount in 1½ cups of cooked penne pasta) per day—and getting 70 percent or more of your calories from fats.
But can eating so much fat really help you lose weight? And even if it does, are there risks that might outweigh the benefits? According to Carol Kirkpatrick, Ph.D., M.P.H., clinical associate professor and director of the Idaho State University Wellness Center, there’s still a lot we don’t know about this diet. “We just don’t have evidence to say that it’s a ‘safe’ dietary pattern to follow long term,” she says. Here’s what you need to know.
What Happens to Your Body
The premise behind the keto diet is that it forces your body to draw energy from the fat in the foods you eat and from stored body fat rather than from carbohydrates.
Usually, your body converts the carbohydrates you eat into glucose, its preferred source of fuel. Your brain, the most active organ in your body, consumes about two-thirds of the glucose you produce, and the rest is used by your other organs, muscles, and cells.
At very low levels of carbohydrate intake, however, your body can’t make much glucose, and your liver begins to convert fatty acids into substances called ketone bodies. The ketone bodies provide an alternative source of energy for your brain and other cells.
You may think of the keto diet as a new trend, but it has actually been around for almost 100 years. Its original purpose wasn’t weight loss, though, but to control epileptic seizures before medications for epilepsy were developed.
Although scientists aren’t completely sure why the diet reduces seizures, even today it’s an option for treating epilepsy in children and adults, says Kelly Roehl, M.S., R.D.N., an advanced-level dietitian and instructor at Rush University Medical Center who works with patients to manage epilepsy, other neurologic disorders, and weight.
What You Eat on a Keto Diet
Typically, the few carbs you eat on a keto diet come from non-starchy vegetables. Roehl says that a meal plan for her clients might include:
- For breakfast, a scrambled egg cooked with butter, heavy cream, feta cheese, spinach, and mushrooms.
- For lunch, a salad made with leafy greens, avocado, a hard-boiled egg, bacon, and crumbled or shredded cheese, dressed with olive oil and red wine vinegar.
- For dinner, spiralized zucchini “pasta” and baked chicken topped with an Alfredo sauce made with heavy cream and Parmesan cheese, or an olive oil and pesto dressing.
- For snacks, almonds, celery and cream cheese, or plain 4% fat Greek yogurt and fresh strawberries.
Keto’s Effect on Your Health
Research suggests that people who follow a keto diet do drop pounds. A 2013 analysis published in the British Journal of Nutrition (BJN) that evaluated 13 studies found that people who adhered to it lost more weight than those who followed a low-fat diet, at least in the short term. And Roehl notes that her patients who follow the diet for epilepsy tend to lose weight as a side effect.
But following this highly restricted form of a low-carb diet may not be worth it for most people. For one thing, some carbohydrates—especially fruits, vegetables, beans, and whole grains—are important parts of a healthy diet and are known to reduce the risk of a number of chronic diseases.
A “well-formulated” keto diet can be effective for obesity and type 2 diabetes control, and can even be used as a first treatment option for these conditions, says David Ludwig, M.D., a professor of pediatrics at the Harvard Medical School and a professor of nutrition at the Harvard T.H. Chan School of Public Health. He notes that more research is needed to determine effects on LDL (“bad”) cholesterol levels and whether there are some people, such as pregnant women, who shouldn’t follow this eating pattern.
Still, the keto diet can be hard to stick to and many people “may not need to go to that extreme to get the benefits,” Ludwig says. Some evidence suggests keto may not be better than other diets for long-term weight loss. According to a recent scientific statement about carb-restricted diets from the National Lipids Association published in the Journal of Clinical Lipidology, very-low-carb diets led to more weight loss than low-fat diets in the short term (about six months), but only when both diet plans also severely restricted calories. And beyond six months, “that difference was essentially gone,” according to Kirkpatrick, who is the lead author of the report, and the two types of diets produced similar results.
The analysis also noted that the initial weight loss from low- and very-low-carb diets appears to be primarily due to loss of body water, and that restricting carbohydrates appears to result in greater loss of lean body mass—meaning muscle—as opposed to loss of fat mass.
The keto diet also has a number of drawbacks. For example, in the BJN study, people who followed the diet had increased LDL cholesterol, the kind of cholesterol that leads to a buildup of plaque in your arteries and can raise your risk of cardiovascular disease.
Feeling foggy or lethargic is common during the first few weeks of following the plan, a result of significantly reducing glucose (which fuels the brain and muscles). It takes a few days for the body to switch over to using ketones for energy.
You may also be more prone to dehydration and electrolyte imbalances, because following a keto diet can cause your body to excrete more water than you otherwise would. There’s an increased risk of kidney stones, and, like other low-carb diets, the keto plan may cause bad breath, constipation, and headaches.