THE KETO DIET CAN certainly sound appealing. You ditch carbs, fill up on fat and still lose weight as the body enters a state of ketosis where it breaks down both dietary and stored fats instead of glucose, or sugar, to produce energy. But don’t let the hype fool you.
Such a diet may not be healthy for you (it’s tied for last place on the U.S. News Best Diets Overall list) and could even give you the ketogenic flu.
The keto flu refers to a host of symptoms, such as malaise, headache and lethargy, that you might feel if you had the actual flu or a cold coming on. Websites that promote keto diets may refer to this as a transient phase – that your body’s just not used to having such a high-fat, low-carb diet, according to Tufts University professor of nutrition Susan Roberts.
Why does this happen exactly? Like most things, it’s not exactly clear.
“Metabolically I’m not quite sure what causes it,” Teresa Fung, a professor at Simmons College and a clinical nutritionist, told Popular Science.
Anyone following a keto diet means they must limit their carb intake to about 20 net grams of carbs or less each day. The standard recommendation is between 225 and 325 grams per day. The diet also encourages a heavy fat intake, and a big cause of dietary inflammation is saturated fat, like what’s found in beef, cream and butter. These types of food are promoted as healthy on the keto diet, yet they’re actually inflammatory nutrients. “We haven’t really got long-term safety established for these diets,” says Roberts, a U.S. News Best Diets expert panelist and founder of the iDiet weight loss program.
Though there hasn’t been specific research on this, the food combinations required of the diet could produce the same kind of inflammation you would have if you were starting to get an illness, Roberts says. Clinical trials involving keto diets have documented side effects like constipation, bad breath, headaches and malaise, and there’s little evidence these symptoms are in fact temporary or transient.
So why try the keto diet at all? People who want to lose weight may think they’re losing a lot during the first two weeks, but they’re actually just losing water weight. “Losing water is not what people who are obese need to lose,” Roberts says. “What they need to lose is fat.”
There are some cases, however, where keto diets are valuable, Roberts explains. These diets are used for epileptic patients who may not respond to medication.
Still, assuming your keto diet is healthy doesn’t necessarily make it true. If your intention is to lose weight and be healthy, Roberts recommends adding back minimally processed grains and legumes to boost your carb levels and likely increase the healthfulness of what you’re doing. You’ll end up with a moderately – but not extremely – low-carb diet.
Roberts notes that the nutrition research community hasn’t coalesced around a single diet to champion, but in her opinion it’s edging toward the thought that a Mediterranean-style, low-glycemic index and moderately low-carb diet is a healthy way to eat.