Modius: get weight off, keep weight off

The average American attempts 7 diets per year. One after the other after the other. The beginning always seems promising. Some weight loss happens and we believe that we’ve found a diet that works, but the diet inevitably fails, and that little bit of lost weight finds its way back onto our bodies. However, we have hope, we persevere, and we try another diet, only to find the same trend happening again.

There are many accounts about how our psychology plays a role in weight regain. Namely that our will-power eventually wanes and we give in to the forbidden fruit.

While psychology is helpful, it’s only half the story. There’s much more going on in our biology that helps us make sense of why dieting and behavioral changes are hard to sustain.

Biology is powerful. Understanding biology allows the mind and body to work together so that we can live a healthy life. So, what’s going on in our biology that makes regaining lost weight so hard to avoid?

According to researchers at Columbia University, there are a couple of key biological mechanisms that contribute to weight regain.

  1. Fat cells & their modification
  2. Hormonal changes
  3. Neurobiological damage

These biological mechanisms make it almost a David & Goliath feat to lose weight and keep it off, especially after being obese.

Let’s do a quick and dirty breakdown of each biological mechanism to better understand what’s going on:  

Numero uno: Fat Cells

Fun fact: not all fat cells are made equal. Fat cells come in many different sizes. A tell-tale feature of obesity is “adipose hypertrophy,” an increase in the diameter of fat cells. As an excess amount of weight is gained, the size of fat cells get bigger. As one loses weight, the diameter of the cells shrink down, however there’s still hyerplasia, an over abundance of fat cells in the body.

So, the size of the fat cells go down, but the number of fat cells remain relatively stable.

Why? Theories suggest that after excessive weight gain there may be a problem with ‘programmed cell death,’ meaning that even though the cell size decreases, the number of fat cells persists.

Other ideas are that as the size of the cells decrease, fat oxidation decreases too. Fat oxidation helps break down fuel that is used as energy, so when this oxidative effect is lessened, the retention of fat remains high.

It’s strange that returning to a small cell size seems damaging to the body, but it actually makes sense. Think of your favorite shirt that fits perfectly. Now imagine your older, bigger brother deciding to play dress up and stretching out the seams. Frustrated and also amused, you wash the shirt in semi-hot water, hoping it’ll go back to normal size. While it may have returned to somewhat the same size, the damage has been done. The seems are looser and the fit is not quite perfect anymore.

That’s the same thing that’s happening in the fat cell. After excessive weight gain, the fat cells that were once a normal size get stretched out past their comfortable capacity. Then, as weight is lost, the fat cell goes back to normal size, but the stretching of the adipose tissue leaves the cells damaged and less efficient. In addition, the number of fat cells remains high, making it oh so easy to regain weight.

Numero dos: Hormonal Changes.

Ok, so about those pesky biological chemicals that we call hormones. How do they play a role? The answer: big time. You thought you left your hormonal problems back in your teenage years? Think again. Hormones rule all.

Insulin. Leptin. Ghrelin. Cortisol. Thyroxine. These are the 5 big players, but there are many, many more.

Let’s start with Insulin.

Insulin absorbs glucose, aka sugar. In overweight and obese individuals, insulin is higher because there’s more sugar in the blood that needs re-uptake. When dieting, insulin levels fall. If insulin levels fall too low, the body will scream for sugar, leading to potential overeating of sugary foods.

Moving on to Leptin. Leptin lives in those fat cells that we talked about earlier. Its job is to signals when you’re full. As one diets and the fat cells become smaller, less leptin gets secreted. This means we feel less full. Alternatively, there’s a theory of leptin insensitivity, suggesting that as we gain weight and continue to eat despite being full, we ignore the leptin signal and eventually become insensitive to its cues and therefore feel less full and satisfied.

Hormone number three: Ghrelin. Ghrelin induces hunger. When talking about Ghrelin, we also have to mention it’s partners: PPY & CCK, hormones that, like leptin, signal fullness. When restricting food intake, Ghrelin will naturally go up, telling the body that it’s hungry. At the same time, PPY & CCK decrease, signalling to the body that it’s not full and could use some fuel. So, satiety goes down and hunger goes up, creating the perfect recipe for overeating and weight regain.

Hormones 4 & 5: During weight loss and restriction, the number of thyroid hormones, such as Thyroxine, decrease. Thyroxine controls the rate of metabolism, so this means that the rate of metabolism slows down, resulting in slower breakdown and more storage of fat. This mellowing of the metabolism induces a stress response in the body. Stress equals more cortisol, and more cortisol equals more appetite and inflammation.

Told you your hormonal days weren’t over. And they’re not going way. Learn to love your hormones.

And now on to the last biological mechanism: Neural Responsivity.


So, let’s get more brainy. After all, the brain is what we’re all about. The brain plays a significant role in food intake. There are three ways in which the brain contributes to weight fluctuation:

  1. Homeostasis
  2. The Reward System
  3. The Inhibitory System

Homeostasis, pretty basic. It’s all about maintaining the status quo according to caloric need. The hypothalamus is the brain part that takes care of this process. This biological process is important, but in our modern world of food excess, it can do more harm than good. The hypothalamus wants to make sure you have enough food, so it’ll encourage you to eat in the presence of food even if you don’t necessarily need it. The hypothalamus makes it really hard to keep weight off because if you’re dieting and there is an abundance of food around you, it’ll scream at you to go get that snack.

The reward system, anchored by dopamine neurons in the mesolimbic pathway, works on the perceived value of food. How much pleasure will you get from that tasty bite or delicious drink? The reward system overwrites anything that the inhibitory system or homeostasis mechanism says, and when it’s activated, food gets eaten. Studies show neural difference, particularly in the mesolimbic pathway, before and after weight loss, suggesting that even after you lose weight your brain structure has changed so much so that the reward circuit tends to be more activate.

And the inhibitory system, found in the dorsolateral prefrontal cortex, controls dietary restraints. Therefore, during dieting, the dorsolateral prefrontal cortex is more active. The ironic thing is that as this inhibitory mechanism increases, so does the reward-circuit. So, the more you restrict your diet, the more you perceive the value of the forbidden food to be greater. This makes it awfully hard to restrain yourself, so even though you try, the dorsal prefrontal cortex eventually gets exhausted and the reward circuit wins.

So now you know that it’s not just a matter of a failing will-power that causes you to regain weight, it’s also a matter of biology. The best way to combat this is to not go on extreme diets, but to make small lifestyle changes that are sustainable. The saying, “easy come, easy go” is quite relevant here. If you lose the weight quickly, you’ll most likely regain it quickly. So, be patient and think outside the box. Instead of dieting, start eliminating foods slowly one by one, do one push-up a day and increase from there, or try using brain training programs and devices to get your hypothalamus working in high order.

Even though it seems like your biology has a lot of power over you, being aware of its effects puts a lot of that power back into your hands. So don’t worry, live & learn on.

Hannah Heimer
Hannah Heimer

I’m a brain enthusiast and yoga fanatic. I work as a researcher at the University of California, San Diego while also running a yoga business on the side.

I use brain research and yoga as a springboard to blog about lifestyle, health, happiness, and how it all relates to your brain.

Just like the nerve cells in our brains, I love making new connections. So, feel free to reach out. For more info on yoga and the brain, take some time to explore