Fat Loss

Last Updated: October 13, 2023

Fat loss occurs when more calories are expended than consumed.

How does fat loss work?

There are three components of total daily energy expenditure: the thermic effect of food (i.e., the energy cost of the digestion, absorption, and storage of dietary macronutrients), basal metabolic rate, and physical activity, which can be subdivided into volitional exercise and nonexercise activity thermogenesis (i.e., the energy expended performing common daily activities such as standing, walking, and fidgeting). For fat loss to occur, energy intake must be less than energy expenditure.

How could diet affect fat loss?

There are no meaningful differences in fat loss between diets that vary in carbohydrate and fat content, as long as their protein and calorie content is equal.[1][2]

Nonetheless, certain dietary factors can influence fat loss via their effects on energy expenditure, hunger, and satiety, and thus energy intake. These include ultraprocessed foods, which have been shown to increase ad libitum energy intake;[3] protein, which has the highest thermic effect of food among the macronutrients, helps to preserve muscle during weight loss (and thus preserve basal metabolic rate), and may reduce hunger and prolong satiety;[4] and fiber, which may also reduce hunger and prolong satiety.[5]

Which supplements are of most interest for fat loss?

Supplements of interest for fat loss typically either increase total daily energy expenditure, suppress appetite, or increase the rate at which fatty acids are released from fat cells. The following are some of the most popular supplements related to fat loss:

Most supplements sold for fat loss are ineffective or there’s not enough evidence in humans to support their efficacy, and some can even be harmful. For example, yohimbine, ephedrine, and caffeine can all induce anxiety in some people.

What different types of prescription weight-loss drugs are available?

Several drugs are currently approved by the U.S. Food and Drug Administration (FDA) to treat overweight and obesity. These include orlistat (trade names Xenical/Alli), phentermine-topiramate (trade name Qsymia), naltrexone-bupropion (trade name Contrave), liraglutide (trade name Saxenda), semaglutide (trade names Wegovy/Ozempic), and tirzepatide (trade name Mounjaro).

Typically, weight-loss drugs are only prescribed to adults with obesity (BMI of 30 or greater) or who have a BMI of 27 or greater and other weight-related comorbidities like hypertension (high blood pressure) or type 2 diabetes.

A drug called setmelanotide (trade name Imcivree) is also approved for weight loss, but its use is limited to people with one of three rare genetic disorders.[30]

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Update History
2023-10-12 00:30:02

Small corrections about body composition

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A reader pointed out a few issues with how we discussed the effect of weight loss drugs on body composition, so we fixed it.

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2023-08-14 13:28:00

Medical review complete

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One of our physician reviewers reviewed this page.

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2023-07-25 16:56:12

New FAQs about weight loss drugs

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We added a bunch of new FAQs related to weight loss drugs to this page.

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