Can I Lose Body Fat in a Week?

A week gives you time to start the process of fat loss and even lose a pound or two. Losing a significant amount of body fat in seven days, though, isn't possible. Your body metabolizes fat over time to cause changes in your body composition. You didn't gain weight in a week, so you can't expect to lose it in such a short period of time.

Choose healthy snacks, such as fruit, during a week-long weight-loss effort. (Image: Courtney Keating/E+/Getty Images)

Fat Loss Basics

You lose a pound when you create a 3,500-calorie deficit between what you consume and what you burn. Whether that pound is fat or mostly water and muscle depends on how much weight you have to lose and how fast you try to lose it. The greater amount of fat you have on your body, the more you can expect to drop in a week's time. If you're quite overweight, like the competitors on weight-loss reality shows, you may lose a lot of fat pounds in a short period of time simply because you have a lot to spare.

A lot of the weight you lose initially is also water weight, not just fat. As your body adapts to a healthier eating plan that includes fewer processed foods containing sodium, you excrete stored fluids. Most diet plans also encourage ample hydration from water to keep your hunger at bay and your body healthy, which can cause you to excrete even more fluids.

Losing Body Fat Effectively

A calorie deficit is necessary to lose body fat. Do so with a combination of exercise and a healthy, whole-foods diet. Exercise should include moderate-intensity cardiovascular exercise -- about 250 minutes per week to experience significant weight loss, according to the American College of Sports Medicine. Check with your doctor before beginning an exercise program, especially if you haven't been active for a while.

In addition, strength train all the major muscle groups at least twice per week on non-consecutive days. Do one or more sets of eight to 12 repetitions of an exercise with a weight that feels heavy by the last couple of efforts. If a weight becomes easy after 12 repetitions, it's time to increase. These are basic guidelines for strength training for health; other strength-training protocols are used for power, size and strength development.

Reducing the number of calories you eat daily also helps you achieve a deficit. Focus on eating plenty of fresh vegetables and moderate amounts of whole grains at meals. Adequate lean protein, such as 20 to 30 grams four times per day, can help you support strength-training efforts to preserve lean muscle. Foods that contain protein and support weight loss include lean meats, skinless poultry, tofu, low-fat dairy, eggs, whey protein and fish.

Fast Weight Loss May Mean Muscle Loss

To keep your metabolism humming for optimal fat loss, don't eat fewer than 1,200 calories per day. Dropping lower than this, even for a week, can lead to muscle loss, especially if you're close to your goal weight. Your body holds onto your fat stores because it fears starvation. Muscle takes more energy for your body to maintain, so it will burn muscle tissue for fuel when you don't have a lot of fat to lose. For the average overweight person, 25 percent of every pound you lose is muscle mass if you don't exercise while following a low-calorie menu.

Losing more than 1 to 2 pounds per week, or even 1/2 pound when you're already rather lean, makes a greater percentage of muscle loss more likely to happen. When you lose muscle instead of fat, you may weigh less on the scale, but your body composition actually tilts toward being fatter. If you aren't drastically overweight and try to lose a lot of body fat or weight in one week, you'll likely not lose more than a few pounds, and what you do lose from extreme measures will be mostly water and lean body mass.

Guidelines for Body Fat Loss

No official guidelines exist on the optimal rate of body fat loss, but the American Council on Exercise puts it at about 1 percent per month, not per week.You may lose body fat in a week, but the amount is so minuscule that you're unlikely to get a legitimate change in a body fat reading such as calipers or a body fat scale. These methods are subject to user error and, in the case of the scale, to hydration, so any wild changes you see are likely a result of an inaccurate measurement. The fat loss may show up in a drop of a pound or two on the regular bathroom scale, though.

A fit, healthy body fat percentage for women is 21 to 24 percent; for men, it's 14 to 17 percent. Athletes can have somewhat lower levels and still be healthy. All people need a percentage of essential fat to support bodily function and cushion internal organs. For men, this level is 2 to 5 percent; for women, 10 to 13 percent.