Entering ketosis is no picnic.
According to Melanie Boehmer, a registered dietitian at Lenox Hill Hospital in New York City, people adopting the diet develop what’s called the “keto flu” as their metabolism shifts from carbs to fats, says. Symptoms can include fatigue, foggy mental function, increased hunger, difficulty sleeping, nausea, constipation or diarrhea.
The keto flu usually sets in three days to a week after starting the diet, and lasts a week to two weeks, Boehmer says. “If it lasts longer than three or four weeks, you’re probably not in ketosis and you’re teetering back and forth” between the two metabolic states, she noted.
The mistake people make that extends keto flu is reintroducing carbs back into their diet too soon, Boehmer said. “The recommendation is to be in ketosis for two or three months before you even start to try and do that,” Boehmer said.
There are some concerns about the effectiveness and healthiness of the keto diet, mainly because there’s not much scientific evidence regarding it, says Cat Taylor, a registered dietitian with Nutrition on Demand, a Washington, D.C.-based consulting firm.
“While there are some small studies supporting the benefits of the keto diet, no substantiated evidence-based research has been published and, most concerning, the long-term impact of the keto diet is unclear,” Taylor said.
Some nutritionists are worried that by shunning carbs, people will miss out on crucial nutrients found mainly in carb-laden fruits and vegetables, Taylor said.
“Several nutrients vital to health are contained in carbohydrate-dense foods, including fruits, vegetables, legumes and grains,” Taylor said. “Just one medium apple contains about 17 grams of net carbs. This is concerning because these vitamins, minerals and phytonutrients contained in the above foods are vital to heath, immunity and disease prevention.”
The keto diet also can be a cardiologist’s nightmare, Taylor added.
“The keto diet’s focus on fat-dense foods is concerning especially if individuals choose a high amount of saturated or trans fats, which are linked to a rise in LDL ‘bad’ cholesterol that has been connected to higher rates of heart disease,” Taylor said.
Foods that can contribute to a healthy keto diet include seafood, grass-fed beef and poultry, no-nstarchy vegetables, avocados and berries, Boehmer said.
“You should focus on whole foods that are naturally low in carbs,” Boehmer said.
One last warning — people taking up the keto diet should not be fooled by quick weight loss early on, Boehmer said. If they start adding in carbs too soon, they will regain the weight and potentially extend their keto flu.
“When you transition to a ketogenic diet, people lose a lot of weight very quickly,” Boehmer said. “That’s not actually because they are losing physical weight. It’s usually because carbs hold more water, so they’re losing water weight. That’s another thing to recognize. You need consistency to see actual weight loss and change.”