Should You Eat Before or After Working Out?

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Studies have shown that your body’s responses to exercise can differ based on whether or not you eat before exercise.

Exercising Fasted Increases Your Body’s Ability to Use Fat for Fuel

Your body’s primary sources of fuel are body fat and carbohydrates.

Fat is stored as triglycerides in fat tissue, while carbs are stored in your muscles and liver as a molecule called glycogen.

Carbs are also available in the form of blood sugar.

Studies show that blood sugar is higher before and during exercise when you eat before working out (1, 2).

This makes sense because most of the pre-exercise meals in these studies provided carbs, which the body used for energy during exercise.

When exercising on an empty stomach, more of your body’s energy needs are met by the breakdown of body fat.

A study in 273 participants found that fat burning was higher during fasted exercise, while glucose and insulin levels were higher during non-fasted exercise (3).

This tradeoff between carbohydrate and fat metabolism is part of your body’s natural ability to function with or without a recent meal (4).

Exercising Fasted May Not Lead to a Greater Loss of Body Fat

Given that your body burns more fat for energy when it is fasted, it’s tempting to think that this will lead to greater fat loss over time.

One study demonstrated different responses in individuals who exercised in the fasted state, compared to those who ate before exercise (5).

Specifically, the ability of the muscles to burn fat during exercise and the ability of the body to maintain its blood sugar levels were improved with fasted exercise, but not fed exercise.

Because of this, some scientists believe that your body’s response to exercising fasted would cause more beneficial changes in body fat than exercising after eating (6).

However, despite some evidence showing potential benefits of exercising fasted, there is no strong evidence that fasted exercise leads to greater weight or fat loss (7).

Although limited research has been conducted, two studies showed no difference in fat loss between women who exercised fasted and those who exercised after eating (8, 9).

Summary

Your body’s response to exercise differs based on whether you eat before exercise. Exercising fasted causes your body to use more fat for energy. However, research does not show that this translates to a greater loss of body fat.

Many people who want to perform at their best wonder if exercising fasted will harm their performance.

Some research has tried to answer this question. One analysis examined 23 studies on whether eating before exercise improved performance (1).

The majority of research showed no difference in performance between those who ate before aerobic exercise lasting less than an hour and those who did not (10, 11, 12).

Other studies examining high-intensity interval training (HIIT) also found no difference in performance between fasted and fed exercise (13, 14, 15).

Although limited information is available for weight training, some research shows that exercising fasted or fed may produce similar results (16).

One reason why clear benefits of eating before short-duration exercise were not seen in these studies could be due to the body’s own stores of energy.

Your body stores approximately 2,000 calories as glycogen and much more in body fat (17, 18).

All that stored energy allows you to exercise even if you have not eaten for hours.

That said, some studies have shown an improvement when carbohydrate-containing meals or supplements were consumed before exercise (19, 20).

Eating prior to short-duration exercise does improve performance in some people, and the best choice probably varies based on the individual.

Summary

The majority of studies do not show a clear benefit to eating before short-duration aerobic exercise or intermittent exercise like HIIT. However, some studies have shown that eating before exercise improved performance.

A large analysis of exercise lasting longer than one hour found that 54% of studies reported better performance when food was consumed before exercise (1).

Most of the studies showing a benefit of a pre-exercise feeding provided a meal composed primarily of carbs.

Consuming slower-digesting carbs or eating several hours before exercise may benefit long-duration performance.

For endurance athletes, other research has shown benefits of eating a high-carb meal three to four hours before exercise (21).

There may also be benefits to consuming carbs in the hour before exercise for long-duration events (22).

Overall, there is stronger evidence in support of the benefits of eating before longer-duration exercise, compared to shorter-duration exercise.

However, some studies showed no benefit of a pre-exercise meal (1).

Summary

While some mixed results have been reported, eating before long-duration exercise is probably beneficial. Recommendations to consume a meal three or more hours before exercise are common, but there may be benefits to eating sooner before exercise.

While the importance of eating before a workout may vary based on the situation, most scientists agree that it’s beneficial to eat after exercise.

Research shows that some nutrients, particularly protein and carbs, can help your body recover and adapt after exercise.

Eating After Exercise Is Especially Important If You Work Out Fasted

If you eat during the several hours before you work out, the nutrients you ingest may still be present in high concentrations in your blood during and after exercise (23).

In this case, these nutrients can aid recovery. For example, amino acids can be used to build up proteins, while carbs can replenish your body’s glycogen stores (24).

However, if you choose to exercise fasted, your body has fueled your workout using its own energy stores. What’s more, limited nutrients are available for recovery.

In this case, it is particularly important that you eat something relatively soon after exercise.

One study examined whether eating a meal containing protein and carbs after fasted exercise led to greater increases in the production of proteins in your body, compared to when no nutrients were consumed (25).

While there was no difference in how much new protein the body made, eating after exercise did reduce the amount of protein breakdown.

How Soon After Exercise?

While eating after exercise is important, some research has shown that it may not be necessary to eat the second you finish working out.

For example, one study examined how well the carbohydrate stores (glycogen) in muscle were recovered after two hours of cycling (26).

During one trial, participants began eating immediately after exercise, while they waited two hours before eating in the other trial.

There were no differences in the muscle’s recovery of carbohydrate stores over the eight or 24 hours following exercise, indicating that waiting two hours to eat was not detrimental.

Other research examining the importance of consuming protein immediately after exercise has shown mixed results.

While some studies show that consuming protein immediately after exercise is beneficial for muscular growth, others show no detrimental effects of waiting several hours (23).

Based on the existing evidence, a reasonable recommendation is to eat as soon as it is feasible after exercise.

Again, eating as soon as possible after exercise may be more important if you do choose to exercise without eating beforehand.

Summary

Getting nutrients in the hours around exercise is important. If you don’t eat before exercise, try to eat soon after exercise. Consuming protein can help repair your muscles and other tissues, while carbs can help restore your glycogen stores.

While studies have illuminated the effects of eating or fasting before exercise, the most important factor may be personal preference.

Eating before exercise may be more important for particular groups, such as high-level athletes and those performing long-duration exercise (27).

However, most active individuals can make great progress when exercising fasted or fed.

Thus, your personal preference about when you eat relative to exercise should play the biggest role in your decision.

For some people, eating soon before exercise can make them feel sluggish or nauseous. Others feel weak and fatigued without having something to eat before working out.

If you exercise in the morning, the duration between when you wake up and when you exercise could impact your choice.

If you head out for a run or to the gym immediately after waking, you may not have time for your food to properly settle before you exercise.

The less time you have between eating and exercise, the smaller the pre-exercise meal should be. This can help prevent feelings of fullness and discomfort during exercise.

As discussed, consuming beneficial nutrients like lean protein and carbs from nutrient-dense foods is important in the hours surrounding exercise.

However, you have the freedom to choose whether to consume these before exercise, after exercise, or both.

Summary

Personal preference should determine whether you eat before or after exercise. Eating before exercise may be more important for high-level athletes and those who exercise for long durations, but most can reap the benefits of exercise regardless.

Whether or not to eat before exercise is a common dilemma, particularly for those who exercise in the morning soon after waking up.

Although exercising without eating first can increase your body’s ability to use fat for fuel, this does not necessarily translate into greater body fat loss.

In terms of performance, there is limited support for the importance of eating before short-duration exercise. Eating before longer-duration activities may be more beneficial.

Eating before exercise may also be more important for high-level athletes who do not want to risk compromising their performance.

While you don’t have to eat before working out, getting nutrients in the hours around exercise is important.

Therefore, if you don’t eat before you exercise, try to eat soon after you exercise.

Overall, personal preference should be the main factor when deciding whether or not to eat before working out.