Exercise for fat loss

Looking to start an exercise program to lose weight? ...Read this first.

Fork with measuring tape wrapped around it like pasta


1. Overview

2. Can you lose weight with just exercise?

3. Does anything work?

4. Learnings

5. References

The gist

  1. Research shows little to no relationship between energy expenditure and body fat levels. (A gigantic study on 34 079 women concluded that, to prevent fat gain with exercise alone, women must exercise for approximately 60 minutes every day. The amount needed to lose fat was undetermined.)

  2. The #1 reason for this is a subconscious increase in food intake. However, a conscious increase in food intake is also a contributor as people who are told they are "exercising" consume 41% more calories than those who are told they are being active for "fun".

  3. A second contributor for some individuals is a reduction in subconscious activity levels away from the gym (termed: NEAT).

  4. Nutrition, and in particular taking control over energy "in", is the missing key to allowing fat loss to occur with exercise.

  5. Nutrition + exercise interventions result in a rate of fat loss that is 3-10x faster than exercise alone. Nutrition accounts for at least 70% of this fat loss.

  6. You should still exercise as it is likely the single most important modifiable determinant of your health and longevity.

  7. If your goal is to lose fat, create a calorie deficit, either through consuming fewer calories than you are now, increasing your activity, or both. Just make sure that you are not re-consuming these calories by not paying attention to your nutrition.

A calorie deficit is required to lose weight [1]. According to the laws of thermodynamics, there are no ifs, ands, or buts about this.

However, many factors affect this energy balance equation that sometimes makes it seem like expectations and reality don’t quite line up. This is because it is more complicated than it seems on the surface. Today we’re going to be discussing how focusing on only one piece of the equation may influence other pieces without you even noticing.

Can you lose weight with just exercise?

Let’s look at some of the largest studies to date on this question:

Preeminent message: Kicking up your energy out without acknowledging your energy "in" rarely leads to any appreciable fat loss. But…What? How? When? Why?

Our #1 culprit: a subconscious increase in food intake.

In fact, we’ve known this for a long time. Over 60 years ago (1956) a study from Harvard concluded: “The regulation of food intake functions with such flexibility that an increase in energy output due to exercise is automatically followed by an equivalent increase in caloric intake” [11].

It appears that people are often completely unaware that they are eating more and that this compensation can happen even a few days after the workout [12].

This means a hard boot camp session on Thursday may cause you to subconsciously choose a very high-calorie meal off the menu at the restaurant on Saturday that you maybe wouldn’t have chosen otherwise. Or, maybe an extra serving of pasta you cooked. Or, maybe just the leftovers on your friend’s plate that they couldn’t finish.

This is not to say that all increases in intake after exercise are a result of subconscious awareness. Certainly, conscious choices play a role as well. Our culture promotes energy-dense highly delicious food as rewards for hard exercise.

Consider this with the results from a study that found that people who went for a walk and were told they were "exercising" consumed 41% more calories from indulgent desserts and drinks following a post-walk lunch than those who were told they were walking for "fun"[13].

One important side note is that although there is an increase in caloric intake when individuals begin exercising, there is also a beneficial effect on appetite regulation [14]. This means that although someone may increase their intake to make up for the energy expended and keep them in energy balance they are also less likely to overeat and gain weight than someone who does not exercise.

Our #2 culprit: Subconscious reductions in energy expenditure away from the gym

If you analyze different populations around the world, like Dr. Herman Pontzer and colleagues did [15], you see that total daily energy expenditure is similar across them. However, this is despite some of them spending far more time exercising.

For example, in Figure 2 of that reference, you can see that hunter gatherers like the Hadza and the Tsimane spend ~110-140minutes/day being physically active and the USA only spends about 20-40minutes/day. Despite this 4-fold difference, there is no difference in the number of calories they expend in 24 hours!

Or, how about this study [16] that looked at one group exercising 2000 calories/week and another exercising 3000 calories/week. Again, despite the marked differences in physical activity there was no difference in total calorie expenditure.

Well then, where is energy expenditure lowering to make up for the increased energy expenditure from exercise? In both of these cases above, these were measuring calorie expenditure from moderate-vigorous. This means there is opportunity at other times during the day to decrease energy expenditure from low intensity activity or simply standing, fidgeting or holding upright posture.

All of this is considered non-exercise activity energy expenditure (or NEAT) and some of us have shown to decrease NEAT levels following exercise [17,18]. Increased exercise with decreased NEAT can mean no change in total daily energy expenditure.

Does anything work!?

Okay, okay we get it, we probably won’t lose fat by just taking up exercise. Stop with the studies! (Sorry I couldn’t help myself). What about diet? Does that even work then?

You’ll see the last study mentioned in the first chart above by Jakicic and colleagues in 2011 stumbled upon physical activity being effective for weight loss only in those who are conscious of their eating behaviours. They found this by seeking out the reason for the difference between those who lost weight and those who didn’t in their population.

In addition to this, there have been a few studies which have directly compared the effects of diet and exercise (E+D) to diet alone (D) and exercise alone (E).

Let’s take a look:

Message: Nutrition, and in particular taking control over energy in, is the missing key to allowing fat loss to occur with exercise.

These studies would suggest that nutrition accounts for at least 70% of fat loss when combining exercise and nutrition.

But the chart shows that diet works alone. Is it even worth it to Exercise? Of course, you should still exercise!

Exercise is likely the single best thing you can do for your health even if no fat loss occurs.

It is not that exercise does not allow you to lose weight, it is that you do not lose weight if you leave caloric regulation completely up to your body.

Regimented exercise can typically result in 100-500 additional calories expended for the average Joe in a day. The exact amount depends on intensity, duration, experience level and current body composition, but any deficit in this range is enough to result in fat loss. However, it is clearly critical not to re-consume these calories as although it can take hours to burn them off it can take seconds to re-add them. And as we’ve learned, this is likely to happen without you even being consciously aware of it!

Other reasons to exercise while trying to lose fat are:

  • Exercise preserves resting metabolic rate compared to diet alone, which enhances the ease of maintaining your losses long term [19,20].

  • Resistance exercise preserves muscle when in a calorie deficit.

  • As shown in the above table, exercise accelerates the rate of fat loss when coupled with nutrition.

I am not the only person who believes regular exercise is the best thing you can possibly do for health and longevity. There is actually plenty of research data to support this [21,22].


"Exercise is the single most important modifiable determinant of health. There is nothing that a person could do that would help and benefit their health more than regularly exercising."

“By continually tying exercise to weight control and weight loss, we do a disservice to exercise because people won’t realize the unbelievable benefits are worth having regardless of weight and we do a disservice to weight management because people are going to try stupid things when they fail with the thing they are told is supposed to help them.”