Ketosis is pretty different from what your body is used to, and this onslaught of symptoms is its way of dealing with carb withdrawal—and adapting, explains Kristen Mancinelli, RD, author of The Ketogenic Diet. “It takes a while, usually a week or two, for the metabolic machinery to shift to fat-burning mode. And you’ll feel pretty crummy while the transition is happening,” she says.

You've likely heard horror stories of what competitors feel like when they cut carbs low, or when the average bro talks about going keto. However, the odds are that those people were not actually in nutritional ketosis, or more importantly, following a well-formulated ketogenic diet. Yes, you may experience some fogginess and discomfort, but it doesn't have to be intense if you handle it right.


As for if you’re dealing with health issues, you really have to defer to your doctor. For instance, if you have kidney disease, you also want to talk to your doctor about appropriate protein intake. If you have heart disease, you can still go low carb, but you may be better off opting for monounsaturated fats (avocados, nuts, and olive oil) over saturated fats (butter and red meat). Everyone’s cholesterol levels respond differently on a low-carb diet, so if yours are going up, switch to unsaturated sources of fats, Spritzler recommends. “In general, this is a diet most people can do. If you have a chronic condition, work with a doctor who understands low-carbohydrate diets to monitor you,” she adds.
Selecting the right food will be easier as you become accustomed to the keto approach. Instead of lean meats, you’ll focus on skin-on poultry, fattier parts like chicken thighs, rib-eye steaks, grass-fed ground beef, fattier fish like salmon, beef brisket or pork shoulder, and bacon. Leafy greens such as spinach, kale and lettuce, along with broccoli, cauliflower and cucumbers, make healthy vegetable choices (but you’ll avoid starchy root foods like carrots, potatoes, turnips and parsnips). You can work in less-familiar veggies such as kohlrabi or daikon.
Here’s what we do know: The keto diet may be useful in treating symptoms of epilepsy, a seizure disorder. “The use of keto in treating epilepsy has the most evidence,” Angelone says. One study conducted by Johns Hopkins Medicine, for example, followed epileptic patients on the keto diet and found that 36 percent of them had a 50 percent reduction in seizures after three months on the diet, and 16 percent were seizure-free. However, experts aren't entirely sure why the keto diet has this affect, she adds.

Exercise training seems to increase this gap even more. In another study, researchers wanted to see the changes that 60 minutes of moderate intensity exercise training would have on free testosterone:cortisol ratio. They split the people into two groups: a 60% carbohydrate diet group and a 30% carbohydrate diet group. The lower carbohydrate group had a 43% decrease in free testosterone:cortisol ratio, while no statistically significant change occurred in the higher carbohydrate group.
In 1994, Hollywood producer Jim Abrahams, whose son's severe epilepsy was effectively controlled by the diet, created the Charlie Foundation for Ketogenic Therapies to further promote diet therapy. Publicity included an appearance on NBC's Dateline program and ...First Do No Harm (1997), a made-for-television film starring Meryl Streep. The foundation sponsored a research study, the results of which—announced in 1996—marked the beginning of renewed scientific interest in the diet.[1]
Adopting a ketogenic diet may also hamper athletic performance, says Weiss, even though many athletes try it, thinking it will have the opposite effect. In a recent study in the Journal of Sports Medicine and Physical Fitness, Weiss and his colleagues found that after four days on a keto diet, participants performed worse on anaerobic exercise tasks—which involve short bursts of intense activity—than those who’d recently gone on a high-carb diet.
The ketogenic diet reduces seizure frequency by more than 50% in half of the patients who try it and by more than 90% in a third of patients.[18] Three-quarters of children who respond do so within two weeks, though experts recommend a trial of at least three months before assuming it has been ineffective.[9] Children with refractory epilepsy are more likely to benefit from the ketogenic diet than from trying another anticonvulsant drug.[1] Some evidence indicates that adolescents and adults may also benefit from the diet.[9]

Yes, ramping up your fat consumption can help speed up the transition of burning fat for fuel instead of glucose. Have a tablespoon of coconut oil in your coffee or tea, snack on half of an avocado and some bacon, and load up on egg yolks at dinner before you reach for the carbs, and remember: the keto flu too shall pass (and the benefits that follow ketosis will be totally worth it in the end).
Heart disease: The diet emphasizes eating a lot of fat. If you eat too much saturated fat (the kind in foods like bacon and butter), that could raise your cholesterol, especially LDL, which is linked to heart disease. This is a special concern for people with diabetes, since the condition itself makes you more likely to get heart disease. Make sure that healthier sources are providing your fats -- the mono- and polyunsaturated kinds, such as those in foods like avocados, nuts, and olive and canola oils. If you do it right, your LDL cholesterol and triglyceride levels could go down. If you take medicine for heart problems, such as high blood pressure, check with your doctor to see if you need to make changes to your medications.
A survey in 2005 of 88 paediatric neurologists in the US found that 36% regularly prescribed the diet after three or more drugs had failed, 24% occasionally prescribed the diet as a last resort, 24% had only prescribed the diet in a few rare cases, and 16% had never prescribed the diet. Several possible explanations exist for this gap between evidence and clinical practice.[34] One major factor may be the lack of adequately trained dietitians who are needed to administer a ketogenic diet programme.[31]
When you eat less than 50 grams of carbs a day, your body eventually runs out of fuel (blood sugar) it can use quickly. This typically takes 3 to 4 days. Then you’ll start to break down protein and fat for energy, which can make you lose weight. This is called ketosis. It's important to note that the ketogenic diet is a short term diet that's focussed on weight loss rather than the pursuit of health benefits. 
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