How Weight Loss Really Works — and How to Get Started

The process of losing weight is simple: Calculate your daily calorie goal, and then adjust your diet and exercise to achieve it. (Image: AndreyPopov/iStock/GettyImages)

There always seems to be a hot, new diet claiming rapid weight loss. Rather than adopting wholesale any given diet or program, however, understanding the actual process of losing weight will help you design a regimen that works best for you.

Calculate Weight-Loss Calories

No one likes to count calories, but the reality is that weight loss requires you to be conscious of the balance of energy going in and out of your body, which is measured in calories. In a nutshell: You must burn more energy than you consume to create the energy deficit required for weight loss.

The size of this deficit depends on how quickly you want to lose weight, which, according to the Centers for Disease Control and Prevention (CDC), should be a gradual process in order to be both safe and sustainable long-term. The CDC recommends aiming to lose 1 to 2 pounds per week, which you can achieve by cutting 500 to 1,000 calories per day, respectively, since a pound of fat contains 3,500 calories.

Subtract this caloric deficit from your Total Daily Energy Expenditure (TDEE), which, according to a study published February 2014 in the Journal of the International Society of Sports Nutrition (JISSN), is the sum of calories used by your body for normal bodily functions, plus additional energy expenditures.

You can estimate your TDEE by adding up the calories your body naturally burns in a day, called your resting metabolic rate (RMR), and other sources of energy burn, according to the American Council on Exercise (ACE), including calories burned doing non-exercise activity. It may be more convenient, though, to use the weight-loss calculator provided by the National Institute of Diabetes and Digestive and Kidney Diseases.

If you want to figure out your RMR on your own, you can use formulas such as the Mifflin-St Jeor equation, below. (Keep in mind that you should measure your weight in kilograms, height in centimeters and age in years, according to ACE.)

Male: 9.99 x weight + 6.25 x height – 4.92 x age + 5

Female: 9.99 x weight + 6.25 x height – 4.92 x age – 161

Subtract 500 to 1,000 calories from your TDEE to determine your daily caloric goal. As an example, if you plan to lose 2 pounds per week and your TDEE is 2,500 daily calories, then you should eat 1,500 calories each day to reach your weight-loss goal.

Cut Your Calories

Next, start cutting calories in your diet, through portion control and/or eating lower-calorie foods. Whatever you decide, it's important to track your calories and follow a meal plan. You can plug your meals into's MyPlate app, which can help you track calories, design meal plans and track your progress.

Weighing foods with a food scale can help ensure that you are hitting your daily caloric and nutritional targets. Cheating on diets is common, and weighing preset portion sizes is one way to limit this problem. "Meal prepping" using recommendations such as those outlined by the Harvard T.H. Chan School of Public Health can take meal planning to a higher level, helping you save money and ensuring you meet your daily caloric goals.

Choose a Weight-Loss Program

Once you've determined your daily caloric goals and have begun tracking your calories, start thinking about a diet plan that considers more than just calories. Some diets focus on specific ratios of macronutrients — carbohydrates, proteins and fats — while others promote eating "clean" foods or avoiding certain food groups.

Low-carb and low-fat diets are among the most popular and most studied. According to a meta-analysis published in the Journal of the American Medical Association in September 2014, both low-carbohydrate and low-fat commercial diets are effective for weight loss.

The study included the Atkins, Zone, Weight Watchers, Volumetrics, South Beach, Slimming World, Rosemary Conley, Ornish, Nutrisystem, Jenny Craig and Biggest Loser diets. The big takeaway? People seeking to lose weight should adopt the diet that they can best adhere to.

Consider trying a commercial diet rather than developing your own, since these weight-loss plans often come with useful resources, guidance materials and a community of dieters that can help you get started and adhere to a long-term strategy.


Consult your doctor before making any major changes to your diet or exercise regimen or starting any weight-loss plan, to make sure the plan is safe based on your health history and any current conditions or medications.

Consider Your Metabolism

In addition to caloric intake, both muscle mass and metabolism play a role in determining your rate of weight loss. According to the Mayo Clinic, your metabolism is determined by the following:

  • Body size and composition. Larger or more muscular people burn more calories at rest.
  • Gender. Men burn more calories than women because they tend to have more muscle and lower body fat.
  • Age. Older people burn fewer calories, since they progressively lose muscle mass with age.

The story on metabolism is much more complicated, however. A person's metabolic rate is also partly determined by genetic makeup, hormonal controls, diet composition and environmental factors impacting lifestyle, sleep, physical activity and stress.

According to the JISSN review study, the metabolic rate adaptively slows in response to weight loss. This adaptation makes long-term weight loss difficult, requiring that you lose weight in an incremental fashion and avoid extreme energy deficits (greater than 1,000 calories per day) to ensure a steady, slow rate of weight loss.

Include Physical Activity

While a healthy diet and calorie deficit are key to weight loss, exercise is also a crucial component.

Aerobic exercise is the most efficient way to burn calories. This includes activities like running, bicycling and swimming. According to the Mayo Clinic, you should include at least 30 minutes of physical activity in your daily routine. However, you may have to dedicate more time towards aerobic exercise in order to meet your daily caloric goal. If you don't have time for a longer exercise routine, split up your workout into 10-minute chunks spread throughout the day.

Strength training, such as weightlifting, should be included at least twice a week, according to the Mayo Clinic, because muscle mass is critical in increasing metabolic rate. Since running a calorie deficit for weight loss not only leads to loss of fat but can also result in loss of muscle, moderate strength training exercises during weight loss regimens can help maintain muscle mass and prevent deceleration of the body's metabolic rate.


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