Our wellness culture has an obsession with weight: the need to control it, and minimize it.  Let’s take a deeper look at the science around it, and how it plays into your actual health.


Despite our society’s obsession with weight, most of us don’t actually have a good understanding of the mechanisms behind it. In fact, research published in 2014 on where the fat goes when someone loses weight was still making recent headlines because the answer is surprising to many, including health professionals.

The scientific answer? It mostly gets breathed out as carbon dioxide, and the rest is excreted as water.

However, part of the reason why questions around weight is still difficult to answer is because of the many different components that actually make up our weight. While the dominant fatphobic narrative would lead us to believe that excess weight is simply fleshy bags of fat, our bones, muscles, organs, fluid status, and partially digested food are all part of the number on the scale. It’s normal for weight to fluctuate by several pounds within a day, mostly due to fluid shifts. Let’s explore some of the most common variables.

1. The relationship between calories and weight isn’t all that simple.

You know that ‘simple’ concept of weight gain when energy intake consistently exceeds energy expenditure, or calories in versus calories out? Well, yes it is true, but let’s pause here.

Despite the simplicity of the concept, it doesn’t mean that eating a set X calories will make a person be Y weight. You’ve probably seen this phenomenon in your day-to-day life—we all seem to know someone who can eat large amounts of food and stay relatively the same weight, while others seem to gain weight even with a small amount of food.

To complicate things even further, when you take in fewer calories than what your body needs, additional mechanisms kick in that slow your metabolism and increase your appetite as your body’s way of keeping you from starving to death.

Trying to track and maintain a certain number of daily calories creates the illusion that your metabolism is consistent from day-to-day, when in fact it is constantly shifting based on new inputs and environments. In Canada and the US, companies are allowed a 20% margin of error when it comes to calories on the Nutrition Facts table. On top of that, studies consistently show that we tend to underreport the amount of calories that we eat, and overreport the amount of calories we burn.

This is just part of the reason why the relationship between calories and weight is not straightforward. But even in experimental settings, where calories in and out are measured obsessively, people don’t gain or lose weight at the same rate. Additionally, after weight gain or loss, we see greater increases or decreases in metabolism, respectively, than is expected.

2. It’s (mostly) in your genes.

Your weight is actually mostly dictated by genetic factors—some estimates put it at up to 70%. This doesn’t mean that our genes decide that we’re going to be at a certain weight range and tries to hold us there; rather, the genes code for different factors that could influence our weight, like the hormones that affect our hunger and fullness cues, how much energy we use to perform different tasks, our metabolism, and how effectively our body uses different fuel sources (i.e. carbs versus fat), just to name a few.

Another way to look at is that your genes determines how your bodies react to different inputs that can affect your weight, which can partly explain why the calories in/calories out relationship is not straightforward. Interestingly, while we tend to “blame” our genes for giving us a “slow metabolism”, most of the genes that have been identified as having an effect on weight have to do with appetite regulation (“calories in”) rather than calories out.

3. When you lose, you gain.

Of course, genetics alone can’t explain the fact that average body weight has been increasing more than previous decades since the 70s and 80s—genetic adaptation simply doesn’t happen that quickly. So, non-genetic factors like food availability, lifestyle, and environment absolutely play a role. However, instead of looking at population-based “solutions” like large-scale changes in food supply or living environments, most weight management efforts put the onus on the individual, which may be producing the opposite of the intended result.

When we take in less energy than what our body uses, additional mechanisms are activated that decrease our metabolism and increase our appetite. While it was often thought that this was a response to weight loss, it’s been observed that these mechanisms can be activated within 24 hours of a calorie deficit.

The most dramatic example of this is the “Biggest Loser study“, where when they measured the metabolism of contestants six years after they appeared on the Biggest Loser, it was still lower than expected for their body composition, even when the contestant had regained all of the weight they had lost on the show. These adaptations, coupled with observation of chronic dieters, have led some researchers to conclude that dieting, or any attempt at weight loss, is actually correlated with weight gain. Given our weight-centric focus in diet culture, it begs the question: has our society’s obsession with weight loss actually contributed to weight gain?

So, where does this all leave us?

In reality, the issue around weight gain only matters when we view higher weights and weight gain as a “problem.” From a population perspective, higher weights are correlated with some negative health outcomes; however, in individuals, BMI is an incorrect predictor of health status about 30% of the time.

While it can be interesting to explore some of the possible mechanisms behind weight gain, it’s more important to explore why this question is being asked in the first place. Whether it’s about health, weight stigma, or simply curiosity,

We won’t find the answer by trying to control or manipulate our weight.

Adapted from the original article.

Vincci Tsui, RD is a former bariatric dietitian turned certified Intuitive Eating counselor and Health At Every Size(r) advocate. Based in Calgary, Canada, Vincci specializes in helping people untangle their messy relationships with food and their body, and works with individuals in-person and virtually through her private practice. Read more from Vincci at