1. You might lose weight—but there's a catch.
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Despite everything you've heard about "calories in, calories out," the links between meal skipping and losing weight are tricky. Some research from Ohio State University suggests you'll drop bad weight in the short term—but you'll eventually gain back dangerous belly fat. More studies suggest the weight you lose may come from muscle, not fat, which is hardly ideal. There are some potentially great reasons to skip meals, but losing weight is probably not one of them.
2. Inflammation calms down.
From arthritis to cancer to heart disease, many major health conditions stem from damage caused by chronic inflammation. Periods of fasting appear to trigger damage-repairing adaptations in your cells, finds a review in the Proceedings of the National Academy of Sciences (read more about the growing fasting trend here). While fasting comes in all shapes and sizes, some inflammation-lowering health perks could accrue after forgoing just one meal, says Valter Longo, PhD, one of the paper's authors and a researcher at the University of Southern California. (Longo's work has also found that periods of fasting may improve the effectiveness of chemotherapy.)
3. You could run low on nutrients.
While skipping a meal here and there—sometimes referred to as "intermittent fasting"—can be beneficial, Longo says harnessing those benefits requires careful planning. Otherwise, you risk nutrient deficiencies linked to fatigue, poor mental function, and other health concerns. If you're considering fasting on a regular basis, consult with a registered dietitian or other nutrition pro to ensure you're getting enough protein, vitamins, minerals, and essential fatty acids in your meals and snacks. (Want to lose belly fat? Build your abs and melt fat with Prevention's Ultimate Flat Belly DVD.)
4. Your risk for some diseases may increase.
If you routinely skip breakfast, you may be headed for trouble, says Leah Cahill, PhD, of the Harvard School of Public Health. One of Cahill's studies found that women who skipped breakfast regularly had a 20% increased risk of developing type 2 diabetes. Another of her studies—this one in men—linked going without a morning meal to heart disease. "Our bodies need to be fed food regularly in order to maintain healthy levels of blood lipids such as cholesterol, hormones such as insulin, and normal blood pressure," Cahill says. "As we sleep all night we are fasting, and so if we regularly do not 'break fast' in the morning, it puts a strain on our bodies that over time can lead to insulin resistance, type 2 diabetes, and blood pressure problems."
5. You're likely to make up for a missed meal with junk food.
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Cornell University researchers found that meal-skippers grab 31% more junk food at the grocery store when shopping hungry, compared with when they had a snack beforehand. Shoppers who hit the aisles during the high-hunger hours between 4 PM and 7 PM also selected a larger percentage of high-calorie options. All this suggests your body may crave crappier food if you skip meals.
6. You may burn more fat during exercise...
A 2013 study in the British Journal of Nutrition found that morning exercisers burned 20% more fat during their workouts when they sweated on an empty stomach. Important to note: How your body reacts will depend on what the rest of your diet looks like and how hard you're going to push yourself during your workout. But if you're fond of light AM workouts, you might benefit from exercising before your first meal or snack, says sports dietitian Lisa Dorfman, MS, RD. Just make sure you eat a nutritious, filling dinner the night before, she says.
7. ...But you might also end up skipping exercise altogether.
Though a morning workout sans food could have fat-burning benefits, the equation changes later in the day. Combine the low blood sugar that follows a skipped meal with the mental and physical demands of work, parenting, and your other daily obligations, and you may find it nearly impossible to exercise after skipping a meal, Dorfman says.
8. You could "bonk" midway through your workout.
Even if you push through your fatigue and hit the gym or trail, skipping a meal can leave you feeling terrible midway through your session. Athletes call it "bonking," and it occurs when low blood sugar saps your muscles and mind of the energy they require to make it through that next mile or rep, Dorfman says. (Avoid the bonk with these 39 best food combos to eat before every type of workout.)
9. You might get sick.
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After exercise—especially long, intense sessions—spikes in cortisol temporarily suppress your immune system. "Consuming carbohydrates during and right after training helps close that window of immunosuppression," says Georgie Fear, RD, author of Lean Habits for Lifelong Weight Loss. The longer you put off refueling, the greater your risk of headaches, fatigue, extreme hunger, and even infection. On the flip side, eating a meal or snack with protein and carbs within 2 hours of exercise replenishes your body's energy stores and provides the raw material to build new muscle, Dorfman says.
