Set-Point Theory and Body Mass

Why is weight loss so hard?

Many people are dissatisfied with their body weight, with as many as 74.6% of American adults reporting that they have tried to lose weight at some point. 

From the perspective of thermodynamics, your body mass is a fulcrum in an energy-balance equation (see picture below). In this model, your body mass is balanced in between the energy you consume from food and the energy you expend. To achieve weight loss, you must enter a state of negative energy balance, where energy expenditure > energy intake.

In theory, losing weight is a simple proposition: simply eat less and move more to shift your energy balance toward this negative state. In practice though, this is incredibly challenging to achieve in the long term, and at least 50% of people who lose weight end up regaining almost all of it back.

Set-Point Theory

The set-point theory explains many of the challenges in achieving weight loss. According to set-point theory, adult body mass tends to remain in an equilibrium range due to a complex regulatory system that involves appetite mechanisms, the amount of physical activity we do, and cellular metabolism. In this set-point range, obesity protects itself.

Specifically, any attempt to restrict food intake to lose body fat will be countered by a shift in appetite mechanisms to increase feelings of hunger, prompting one to increase energy intake. In addition, losses in body mass lead to a decrease in resting metabolic rate, which decreases total energy expenditure and makes it harder to achieve a negative energy balance.

The set-point theory makes the process of losing weight appear daunting.

However, there is some evidence that the set point is not set in stone. A good challenge to set-point theory is that it fails to explain why we have seen an exponential increase in obesity rates in many countries since the 1980s. This shows us that the equilibrium body weight around which we gravitate can be changed by our environment.

Alternately, the “settling-point” theory has been proposed, in which the role of outside influences such as environment and socio-economic factors on energy intake and physical activity and the consequent development of obesity is recognized. 

So what is the answer?

Finding the optimal strategy for your eating and exercise plan is a lifelong experiment you conduct on a single subject: yourself!

My advice is to recognize that extreme changes in diet and activity will be countered by your genes and appetite mechanisms, so I personally have always favored implementing gradual changes. For example, when trying to lose weight, I would recommend reducing daily energy intake by ~300 kcal per day, in an effort to avoid shocking your hunger hormones and preserving as much fat-free mass as possible.

Recognizing environmental influences on body mass is also worthwhile. Look for ways to provide yourself the opportunity to get more physical activity in ways that you enjoy each day. Emphasize ways to be healthy that you enjoy, so it feels less like a chore and more like you are simply practicing good self-care. 

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