What Happens In Our Body When We Lose Weight?

In Part 1 of our 3-part series, we discussed 10 causes of weight gain and recognized that weight is complex and highly regulated by our biology and our brain. In part 2, we discussed what happens inside the body when our adipose tissue (fat tissue) storage capacity is exceeded and why this contributes to the development of numerous medical conditions. In today’s blog, Part 3, we’ll discuss what happens inside our body and our brain when we lose weight. This is important to discuss, since it is the primary reason why most people regain the weight they lose, and often end up gaining even more weight than they had initially lost, causing the all-too-common yoyo-dieting effect.

As we discussed in our previous blogs, the human body and brain has been developed over millions of years to protect us from weight loss, since this was a common reason for our demise for the vast majority of human history. Your brain does not know whether your weight is a “healthy” weight for you. All it knows is what your weight is. This becomes your “setpoint” weight, and the weight that your brain will fiercely defend if your weight is reduced below your setpoint. Your brain does have defenses against weight gain as well, but these defenses are not nearly as strong. We see the same thing with blood sugar: you can’t feel high blood sugar, unless it becomes severe, but low blood sugar? You feel that right away! The same is true for weight.

When you lose weight, especially once you get to around 10% body weight loss, your brain starts to freak out. It can tell that you are losing weight because as your fat tissue declines, your fat cells produce less leptin. Leptin is the hormone that informs your brain of your fat stores, so when these levels decline, and they decline rapidly with weight loss, your brain begins its efforts to protect you from further weight loss and tries to encourage you to regain the weight you lost.  Reductions in muscle mass, as is commonly seen with weight loss, also gives your body the signal that it’s time to slam the brakes on this weight reduction and time to ramp up effort to regain weight.

How does your brain try to make you regain the weight? It increases the hormones that make you hungry and reduces the hormones that make you feel full. The result? An increase in appetite. No matter how much willpower you have, your biology usually wins out. Like holding your breath: you can consciously hold your breath for so long, but eventually the biologic signals become too strong, and you take a breath. Your appetite signals are equally as strong, but less immediate. And unlike breathing, we make choices about the types of foods we eat, and most of the time we assume that these choices are made under our total, conscious control. Thus, we blame ourselves for lack of willpower when we give into our desire to eat. While we still have a personal responsibility to make the healthiest food choices for ourselves, we also must recognize that there are other, strong, factors at play. We won’t get into food marketing or how food companies make their foods to hijack our brain, but these are also important contributing factors.

So, how long do these changes in hormones that make us hungrier after weight loss last? A month? Six months? Until we regain the weight? We don’t exactly know yet, but from the studies we do have, it appears that these changes last for over a year, even when the weight is regained.

Changes in appetite hormones is just one way that the body tries to protect us from weight loss. The other mechanism with which the body fights weight loss and promotes weight regain is by affecting our metabolism, or in other words, how many calories our body expends. Metabolism slows down with weight reduction, approximately 15% below what would be expected from just the weight reduction itself (in other words, the less you weigh, the less energy you need, but the reduction is metabolism is 15% below what would be expected for the person’s new weight). Our muscles become more efficient, so that we burn fewer calories doing the same activities.

The longest study on this phenomenon, often referred to as the “metabolic handicap”, lasted 6 years, and was performed with contestants from the reality show “The Biggest Loser”.  They found that the metabolic handicap persisted, even 6 years after the initial weight loss, and even if the weight was regained. There was also a great deal of variability between the contestants as far as how much their metabolism slowed, and it’s no surprise that those whose metabolism slowed the most regained the most weight, and those whose metabolism didn’t slow were able to maintain much of their weight loss, and some were even able to continue to lose more weight. So again, was it willpower that allowed some contestants to fair better long term? Or was is biology?

For some people, hearing this news gives them great relief. For years they just blamed themselves and beat themselves up for their inability to lose weight and keep it off, despite multiple serious efforts. For others, this information makes them feel hopeless.

Here is the good news: this is where the science of weight comes in. We now have evidence-based solutions that can help us overcome this biology. These solutions come in the form of nutrition therapy, physical activity, medications, devices, and even surgery. There IS hope. There are REAL solutions to these problems. Not everyone’s body will respond equally as strong to weight reduction, but if you are one of the 90% of people who has tried to lose weight in the past only to regain it, know that there is hope and there are answers for you, and that it’s not all your fault.

Find an obesity medicine specialist under the “Find a clinician” tab on the obesity medicine association website (www.obesitymedicine.org), or https://obesitymedicine.org/find-obesity-treatment/

You can also search for a provider on the Obesity Action Coalition website: https://obesitycareproviders.com/

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