Those issues can be part of what's known as the “keto flu,” Warren says. Other side effects of the keto diet, all of which are tied to carb withdrawal, can include lightheadedness, nausea, mental fog, cramps, and headaches, in addition to tiredness. Luckily, the keto flu doesn't usually last more than a week—which is coincidentally about when people start to see the number on the scale go down, says Warren.
Participants were recruited from the Durham Veterans Affairs Medical Center (VAMC) outpatient clinics. Inclusion criteria were age 35–75 years; body mass index (BMI) >25 kg/m2; and fasting serum glucose >125 mg/dL or hemoglobin A1c >6.5% without medications, or treatment with oral hypoglycemic agents (OHA) and/or insulin. Exclusion criteria were evidence of renal insufficiency, liver disease, or unstable cardiovascular disease by history, physical examination, and laboratory tests. All participants provided written informed consent approved by the institutional review board. No monetary incentives were provided.
Cons: In our experience, capping your calories low will probably mean a lot of internal strife and stress. Plus, we’re big fans of enjoying food instead of fearing it, and 800 calories doesn’t leave much room for satisfied taste buds. Lastly, if you’re currently eating double to triple this amount of food, dropping to a daily caloric intake this low can tank your metabolism and actually slow weight loss more than switching to one of these other diets might. (Curious? Here’s why starving yourself won’t help you lose weight.)
Trim Portions. If you did nothing else but reduce your portions by 10%-20%, you would lose weight. Most of the portions served both in restaurants and at home are bigger than you need. Pull out the measuring cups to get a handle on your usual portion sizes, and work on paring them down. Get instant portion control by using small bowls, plates, and cups, says Brian Wansink, PhD, author of Mindless Eating. You won't feel deprived because the food will look plentiful on dainty dishware.
Wolfrum said he and his colleagues don't want to stop people from changing their diet if that's what's necessary to reach a healthy weight, but they think it's important for people to know that "the [final] verdict on the ketogenic diet is not out yet." There's still more research to be done to fully understand the long-term effects of a high-fat, low-carb diet. In the meantime, said Wolfrum, "more balanced food intake is probably the healthiest way to live."
At the conclusion of the intervention, both groups had improved in all metrics but “these changes were more significant in subjects who were on the LCKD as compared with those on the LCD.” . As a result, the researchers supported the study outlined above and concluded that their “…study shows the beneficial effects of a ketogenic diet over the conventional LCD in obese diabetic subjects.” 
Cyclical keto diet: The Bulletproof Diet falls into this category. You eat high fat, low carb (less than 50 grams of net carbs a day) five to six days of the week. On day seven, you up your carb intake to roughly 150 grams, during what’s called a carb refeed day. Carb cycling this way helps you avoid the negative effects some people experience when they restrict carbs long term, like thyroid issues, fatigue and dry eyes. Learn more here about how carb cycling works.
While reading the weekly meal plans I could close my eyes and picture enjoying the tastes of these dishes while soaking in the awesome summer weather on the patio with my girlfriend, with a glass of my favorite California red wine. “The diet also recommends four ounces of red wine in the evening with your meal. Red wine contains flavonoid which helps reduce your risk of developing cardiovascular disease. That’s my favorite part,” shared Susan.
Over 8–10 mmol/l: It’s normally impossible to get to this level just by eating a keto diet. It means that something is wrong. The most common cause by far is type 1 diabetes, with severe lack of insulin. Symptoms include feeling very sick with nausea, vomiting, abdominal pain and confusion. The possible end result, ketoacidosis, may be fatal and requires immediate medical care. Learn more