As much as you might like to be able to lose weight and get a flat stomach simply by doing sit-ups, this isn't likely to happen. Sit-ups are a resistance exercise, not an aerobic exercise. They help to tone your muscles but don't burn a ton of calories or fat or lead to significant amounts of weight loss. This isn't to say you shouldn't do them while you're trying to lose weight, but remember that you'll need to take other steps as well for noticeable results.
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Calories Burned Doing Sit-Ups
The number of calories burned by doing any particular exercise depends on the weight of the person and how vigorously she does the exercise. Doing about 30 minutes of moderate calisthenics, such as sit-ups, will burn about 135 calories for a person weighing 125 pounds; 167 calories if you weigh 155 pounds; and about 200 calories if you weigh 185 pounds. For each pound of weight loss, you need to create a calorie deficit of about 3,500 calories, so it would take an extremely high number of sit-ups to really make a difference in your weight. A classic study published in Research Quarterly for Exercise and Sport had participants do a total of about 5,000 sit-ups over the course of 27 days without recording any significant change in body weight or body fat.
Resistance Training and Weight Loss
Even though resistance-training exercises don't burn a lot of calories themselves, they're still recommended during weight-loss diets. Otherwise, about 25 percent of any weight that you manage to lose will come from muscle instead of fat. Resistance training helps you build more muscle and retain what you already have, which helps with weight loss because muscle takes more calories to maintain than fat. Combining a reduced-calorie, high-protein diet with resistance training increases weight loss results, according to a study published in Diabetes Care in 2010. The Department of Health and Human Services recommends that adults fit at least two resistance training sessions in each week. Aim to do not just sit-ups but at least eight to 12 repetitions of eight to 10 different exercises to target the different muscles in your body.
Adding Aerobic Exercise to Lose Weight
Adults should get at least 150 minutes of moderate aerobic exercise each week, but if you're trying to lose weight, you may need to get twice that amount. An hour of high-impact aerobics can burn over 500 calories for a 155-pound person, which is about the number of extra calories you need to burn each day to lose about 1 pound per week. Those who are trying to flatten their stomach will be happy to learn that a study published in Medicine and Science in Sports and Exercise in 2003 found that exercise-induced weight loss preferentially targets fat in the stomach.
Making Dietary Changes to Lose Weight
Don't skip meals to try to lose weight, as this could backfire and have you eating even more calories overall. It's better to eat about three meals and a snack each day, with each meal consisting of 2 or 3 ounces of lean protein, the same amount of whole grains and 1/2 to 1 cup of each vegetables and fruits, recommends FamilyDoctor.org. Concentrate mainly on whole foods, and limit highly processed foods and foods high in saturated fats or sugar. Make sure to have a mix of high-protein and high-fiber foods in each meal, as these two nutrients help increase satiety. Even better, follow a low-glycemic-index, high-protein diet, which a study published in the New England Journal of Medicine in 2010 found was the most effective combination for weight loss. Foods that are low-GI don't cause large spikes in your blood sugar levels -- which prevents blood sugar crashes that make you feel hungry -- and include foods that are high in fiber or low in carbohydrates. Highly processed foods and those that are cooked for long periods of time tend to be higher on the glycemic index.
Potential Safety Issues
Some people experience pain in their lower back when they do sit-ups. This could be because you're performing them incorrectly or because of the hard ground pushing into your spine while you do the sit-ups. Doing too many sit-ups without working out the opposing muscles can also overtighten your hip flexor muscles, which can then pull on your back muscles and cause the pain. Traditional sit-ups actually work the hip flexors more than the abs. If this is a problem for you, try other exercises that work the core, such as the front or side plank, along with the glute bridge to stretch the hip flexors.