Fairly recently, the diet was introduced as a weight-loss diet by an Italian professor of surgery, Dr. Gianfranco Cappello of Sapienza University in Rome. In his 2012 study, about 19,000 dieters received a high-fat liquid diet via a feeding tube inserted down the nose. The study showed an average weight loss of more than 20 pounds in participants, most of whom kept it off for at least a year. The researchers reported a few minor side effects, like fatigue.
Other kinesiologists think the keto diet could have dangerous effects on athletic performance, and it's tough to know what potential side effects a long-term high-fat diet might have for a healthy person, since we don't have any solid study results yet. Low-carb diets like keto can make it easy to neglect key nutrients like magnesium, calcium, and potassium found in fresh, high-carb foods like beans, bananas, and oats.
Apples contain pectin, an ingredient that naturally slows digestion and encourages feelings of fullness. Studies show that eating a whole apple with your meal (as opposed to apple juice or applesauce) is a natural appetite suppressant, helping you consume fewer overall calories without feeling deprived. Sass likes using shredded apple in slaws and stir-fry, or mixing them into burger patties to add moisture.
Military diet-approved foods aren't what you'd typically think of as "diet" fare, including hot dogs, toast, ice cream, and canned tuna, says registered dietitian Brooke Alpert. See the full breakdown of the diet meals below. These same meals are prescribed for everyone observing the diet and are carefully planned out so you don't overindulge or stray off the diet (since you can only eat the foods recommended below), says Alpert.
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.
"The issue with exercising during the diet is that you are cutting a large number of calories (your body's source of energy) out of your diet, which may make you feel less energetic and a little more sluggish than your typical self," said Mike Mullen, a performance expert and certified strength and conditioning coach from the New York Sports Science Lab.
Boredom is dangerous and so easily leads to weight gain. While free time gets perceived as relaxing, it actually makes me feel anxious, which can lead to bad eating habits. My busiest days are the ones when I tend to focus less on my food and more on what I need to get done. That's why I always try to fill my schedule with things that make me feel productive—so I don’t find myself rummaging through the pantry for a lack of something to do.
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