How to Lose 20 Pounds in 3 Months With Exercise

If you're overweight, losing as little 5 to 10 percent of your body weight can improve your cholesterol, lower blood pressure and decrease your risk of diabetes, according to Nadia B. Pietrzykowska, MD, FACP. If you have more to lose, surpassing that number can bring you even greater benefits.

With the right exercise program — and a healthy diet — most people can easily lose 20 pounds in three months.

Slow and steady weight loss is more sustainable over time than dropping a lot of weight in a short period of time. People who lose weight gradually are more successful at keeping the weight off, advises the Centers for Disease Control and Prevention (CDC).

Losing 20 pounds in three months is an ideal goal. That means losing a little more than 1.5 pounds per week. According to the CDC, losing 1 to 2 pounds a week gives you the best weight-loss results in the long-term.

Weight loss is a complex process that is affected by many factors, including genetics, hormones, medical conditions and medications, sleep quality, stress and more. But the basic concept is that a calorie imbalance over time leads to fat gain.

Calories are energy from food that your body uses to power all your physiological processes and support the effort you expend on daily activities of living and exercise. Getting enough calories is crucial for optimal, healthy functioning.

However, when you take in more calories than your body needs to support those functions, it can't use them — so it converts them to fat and stores them in fat cells throughout your body. To lose fat, you have to reverse this process.

A calorie deficit means you provide your body with less than the amount of calories it needs each day. This sounds like it would be a bad thing, but it's not when you have excess fat storage. Your body can draw the energy it needs from stored fat. When there is no longer a calorie surplus, you'll start to lose weight.

One longstanding theory is that 1 pound of fat contains 3,500 calories. Therefore, if you burn 3,500 calories, you'll lose a pound of fat. If this theory holds true, you would lose your goal of a little over 1.5 pounds a week by creating a calorie deficit of about 5,688 calories weekly, or 813 calories per day.

This rule likely applies only for short-term weight loss, however, according to Densie Webb, Ph.D., RD. Over time, weight loss can stall and be impacted by other factors that make the rate less predictable. But to lose 20 pounds in three months, you can use this rule as a rough guide.

There are two ways to lower your calorie intake below your caloric needs: diet and exercise. Your diet plays the largest role. Cutting out unhealthy sugary, fatty, fried and fast foods can automatically reduce your calorie consumption significantly — especially if you eat a lot of those foods.

Exercise should come second to diet. You can exercise all you want, but if you're eating an unhealthy diet, it will be difficult — if not impossible — to reach your weight-loss goal.

Still, exercise is a great way to deepen the calorie deficit, and it's good for your health. Two types of exercise should be a part of your program: aerobic exercise and strength training. Aerobic exercise burns calories while you're doing it, and building lean muscle mass through resistance training helps rev your metabolism so you burn more calories around the clock, even when you're not exercising.

Read more: 15 Tips From Real People Who Succeeded at Losing Weight

How much exercise are you currently getting? According to Health.gov's Physical Activity Guidelines for Americans, adults should get at least 150 minutes of moderate-intensity exercise or 75 minutes of vigorous exercise every week. This is the minimum amount necessary to reap the benefits of physical activity.

In addition to weight loss, this amount of activity each week decreases your risk of heart disease, stroke, hypertension, Type 2 diabetes, some cancers, anxiety, depression and Alzheimer's disease. For even more benefits, the Physical Activity Guidelines recommends getting up to 300 minutes a week of moderate-intensity exercise or 150 minutes per week of vigorous exercise.

The best type of exercise for weight loss is any activity you enjoy doing. That ensures you'll do it regularly. If you like moderate-intensity exercise, you can walk briskly, ride your bike at a pace of less than 10 miles per hour on flat terrain, ballroom or line dance, play doubles tennis or practice an active form of yoga like vinyasa or power yoga, says the Physical Activity Guidelines.

If you enjoy a little more intensity, you can jog or run, swim laps, cycle faster than 10 miles per hour, jump rope, hike uphill or with a heavy pack, or do high-intensity interval training.

You can also do a mix of both, perhaps running on one day, doing yoga another and taking a dance class the next. Keeping variety in your routine means it never gets boring, and it also protects you from repetitive stress injuries that result from doing the same activity all the time.

The Physical Activity Guidelines also recommends a strength-training component in an exercise program. Strength training involves working your muscles against resistance, which makes them grow stronger and larger. Having more muscle mass and strength not only increases your resting metabolism, it can also help you maintain your existing muscle mass while you are losing fat.

Aim to train all your major muscle groups — chest, shoulders, back, arms, core and legs — twice weekly. There isn't one single best type of strength training workout for losing fat. However, a challenging program that is progressive — meaning it gets harder over time — is more effective than one that doesn't challenge you and doesn't change in difficulty.

Read more: 7 Unexpected Reasons Why You're Not Losing Weight

You don't even need weights to do effective resistance training. Especially if you are just starting out, you can use your own body weight as resistance. Squats, lunges, pushups, pullups, inverted rows, planks and crunches will target all your major muscle groups. Do enough reps and sets so that your muscles are very fatigued by the final repetitions.

If you have some weight-training experience, you might prefer to lift heavier weights for fewer repetitions. Generally, this will lead to even greater hypertrophy — muscle growth — and strength gains. Compound exercises that work more than one muscle group at a time are better for fat loss because they burn more calories while you're doing them. At the right intensity, compound lifts can also lead to something called excess post-exercise oxygen consumption, or EPOC, in which your body continues burning calories at a greater rate for a period of time following your workout.

Examples of compound exercises for your workout include weighted squats and lunges, dead lifts, bench presses, lat pulldowns, shoulder presses and barbell rows. A general recommendation is to do three to five sets of eight to 12 repetitions per exercise, resting for one to three minutes between sets.