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 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, in which energy expenditure exceeds 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 within an equilibrium range due to a complex regulatory system involving appetite mechanisms, physical activity, 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 that increase hunger, prompting one to increase energy intake. In addition, losses in body mass reduce resting metabolic rate, thereby lowering total energy expenditure and making 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 obesity rates have increased exponentially in many countries since the 1980s. This shows us that the equilibrium body weight around which we gravitate can be changed by our environment.
Alternatively, 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 counteracted by your genes and appetite mechanisms, so I have always favored making gradual changes. For example, when trying to lose weight, I would recommend reducing daily energy intake by ~300 kcal per day to avoid shocking your hunger hormones and preserve as much fat-free mass as possible.
Recognizing environmental influences on body mass is also worthwhile. Look for opportunities to get more physical activity each day in ways you enjoy. 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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