So, you think it is a good idea to increase your metabolism, and you have so far failed to lose weight.

Let me tell you bluntly that this is one of the most tragic myths about weight loss. In fact, boosting metabolism is not correlated with weight loss. Looking to increase metabolism for weight loss is largely a waste of time, and it is probably not good for your long-term health.

It is not usual that you hear this advice from the health “experts” out there who are pitching for the best ways to increase metabolism for the purposes of weight loss. The science, however, does not support it.

Slow Metabolism and Weight Loss

In the previous article on Intermittent Fasting and Weight Gain, we explained the “rebound phenomenon” whereby weight is gained when diet plans are abandoned. That happens because metabolism takes longer to adjust higher than the weight gain caused by higher insulin levels.

How a diet works to slow down metabolism

For dietary interventions, it is important to understand that causality is reversed. It is not that a changing metabolism causes a change in weight. Rather, it is a change in weight that triggers a change in metabolism. The sequence of events in most diet plans that fail is as follows:

  1. Dietary sources of calories are reduced.
  2. The liver begins to break down stored fat to compensate for the energy deficit.
  3. After a prolonged deficit, the body responds by reducing energy expenditure (slows down metabolism).
  4. The body reaches a homeostasis, in which energy expenditure = energy intake.
  5. Everything is in balance, and weight stabilizes at a lower level.
  6. The diet is abandoned, and calorie intake of carbohydrates increases.
  7. Energy intake > energy expenditure and insulin spikes signal fat cells to absorb excess glucose.
  8. Weight gain overshoots the previous weight before the diet was initiated.
  9. Process of weight gain continues until metabolism increases to a level where energy expenditure = energy intake
  10. The body reaches a homeostasis, in which energy expenditure = energy intake.
  11. Everything is in balance, and weight stabilizes at a higher level.

Read steps 5 and 11 again, and you will begin to understand why slow metabolism and weight loss are linked, which means that higher metabolism is linked weight gain.

Slow metabolism and weight loss

Slow metabolism is not what is behind obesity

In fact, most slim people have a slower metabolism than overweight people, and this makes sense from a biological perspective. The body strives to reach homeostasis, where there is a balance between inputs and outputs.

Energy expenditure includes unmetabolized energy

It is very common for a thin person with slower metabolism to consume more calories than an overweight person with a higher metabolism with both being in homeostasis and having stable weights over time.

With some diets, the macronutrient composition takes care of the output part without having to rely on energy expenditure. Under a ketogenic diet, for example, insulin levels are kept low, and very little fat is stored. Dietary fat is excreted in fecal matter. Unmetabolized energy is also output into the environment through urine, methane, heat, and respiration.

Unmetabolized energy is low under high carbohydrate diets

In low-fat high-carbohydrate diets, insulin levels are chronically elevated. This is the body’s reaction to excess glucose in the blood, which is toxic and has to be mopped up by liver, muscle and fat tissue.

Higher insulin levels mean that most of the energy intake is absorbed. Over time, this works to increase weight, and the body’s energy expenditure requirements also rise. Therefore, low-fat high-carbohydrate diets tend to increase metabolism as well as weight.

Weight Loss and Exercise

What about exercise?

We have often heard the advice to exercise in order to increase metabolism. This again misses the point of correlation between high metabolism and weight gain. How many miles on the treadmill do you have to run to burn that extra bowl of cereal?

That is about 5 km or half an hour of running for an average person. That’s the cost of burning that extra 400 calories from a bowl of cereal.

The impact of exercise on weight loss is minimal

In terms of calories, it takes a lot of exercise to burn through small quantities of food that we take for granted. Therefore, the energy expenditure is not as dominated by exercise as people might like to think.

This is made even more complicated by the fact that exercise increases appetite. It is more likely that running 5 km will increase calorie intake such that any weight loss is negated.

Exercise can increase muscle to fat ratio

While exercise may have a very little impact on weight loss, the good news is that it does increase muscle mass. To some extent, the increase in muscle mass does increase metabolism. Keep in mind, however, that this energy expenditure is typically matched by an increase in energy intake to keep the body in homeostasis. Otherwise, weight drops and metabolism slows to achieve equilibrium.

The importance of a good night sleep

While we barely understand the underlying processes of sleep, we do know that it is necessary for maintaining metabolic health. Sleep works to regenerate cellular tissue through a process called autophagy. Damaged proteins are broken down and stem cell activity increases around the damaged tissue to generate new cells.

If this sounds familiar, it is because the process is similar to the one the body goes through during the low-calorie phase of an intermittent fasting diet plan. The body enters a low metabolic state in which the liver begins to synthesize glucose and ketones in the absence of dietary sources of glucose. When glycogen stores are depleted, the body begins to catabolize muscle and organ tissue, prioritizing the damaged ones first.

Other factors influencing metabolic rate

So far the discussion was strictly in relation to body weight and metabolism and assumed all other factors to remain equal. For the sake of completeness, however, the following are additional factors that we may have no control over:

  • Age
  • Gender
  • Genetics
  • Illness and disease
  • Medications

Perhaps we can find alternatives to life-saving medications, and we may one day crack the genetic code for weight control. But for the most part, these are not the factors we can target to reduce weight.

Final Thoughts

It is a fact that an increased metabolic rate goes hand-in-hand with increased oxidation. Increased oxidation causes oxidative stress and damages cellular tissue over time. Across all species, each unit of cellular tissue expends approximately the same amount of energy before it dies. Therefore, it makes sense that human lifespan is limited by the aggregate energy metabolism needed to maintain homeostasis.


Olshansky S. J. and Rattan S. I. (2005). What determines longevity: Metabolic rate or stability? Discov Med. 5, 359-62.

Speakman J. R. (2005). Body size, energy metabolism and lifespan. J. Exp. Biol. 208, 1717–1730.