Weight loss can be intentional, such as from dieting and exercise, or unintentional and be a manifestation of illness. Weight loss can result from a decrease in body fluid, muscle mass, or fat. A decrease in body fluid can come from medications, fluid loss, lack of fluid intake, or illnesses such as diabetes. A decrease in body fat can be intentionally caused by exercise and dieting, such as for overweight or obesity. Weight loss is normal after pregnancy. Other causes of weight loss include, but are not limited to, cancer, viral infection (such as CMV or HIV), gastroenteritis, parasite infection, depression, bowel diseases, and overactive thyroid (hyperthyroidism).
Starving yourself is certainly not a good idea. But if you're otherwise healthy, a brief period of extreme calorie restriction isn't likely to hurt you. You should tell your doctor what you're doing, and be sure to include protein in your diet (70 to 100 grams per day). Take a multivitamin, and eat potassium-rich foods (tomatoes, oranges, and bananas).
While many people turn to artificial sweeteners in a misguided attempt to whittle their waistlines, those fake sugars are likely to have the opposite effect. According to researchers at Yale, artificial sweeteners are actually linked with an increased risk of abdominal obesity and weight gain, possibly because they can trigger cravings for the real stuff and spike insulin levels in a similar fashion to real sugar.
“A study published in Nutrition Journal found that participants who ate foods high in monounsaturated fats for lunch (in this case, half an avocado) reported a 40 percent decreased desire to eat for hours afterward. Monounsaturated fats from sources like olive oil, nuts and avocados can reduce cholesterol, promote weight loss, even boost memory.” — David Zinczenko, author of the  Zero Belly Cookbook
Keeping a toothbrush handy can do more than polish up that smile (and counter the effects of all that belly-slimming garlic); brushing your teeth throughout the day can also help you ditch that belly fat fast. A study conducted a sample of over 14,000 participants found that brushing after every meal was linked to lower weight. That minty toothpaste flavor not only clashes with virtually every food, brushing may also trigger a Pavlovian response that tells your brain the kitchen’s closed.

Even if you do meet your goal, it's nearly impossible to keep off the weight over the long term: "The amount of restriction required [to maintain that number] will make you so hungry that you’ll eat everything in sight—it’s survival instinct," Dr. Seltzer says. And since calorie restriction gradually slows your metabolism, your body will be less prepared to burn the foods you binge on, he adds. That could mean gaining more pounds than you lost in the first place.
Jennette Fulda is a writer, web designer, and weight loss blogger. Jennette used her blog (previously named Pasta Queen) as a place to stay motivated and hold herself accountable throughout her weight loss journey. At one point in her life, Jennette weighed 372 pounds before losing almost 200 pounds through a healthy diet and exercises program. In addition to her blog, she has also documented her journey in two books, a memoir titled “Chocolate & Vicodin: My Quest For Relief From The Headache That Wouldn’t Go Away”, and “Half-Assed”.
Because men are larger than women on average and have more muscle to support, men can usually eat more calories while still losing weight, compared to women. Portion control may be especially important for women. In one study, women who ate smaller portions of food (and less food overall) had lower BMIs than women who limited or avoided a certain type of food.2 This approach seems to work better for women than men.3
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