These under-the-radar chemical messengers can make or break your weight-loss efforts. Here's how to make them work for you.

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Our series, Hormones & Our Health: How What You Eat May Affect How They Work, explores the vast role hormones play in the body and the diet and lifestyle factors that help them function as they should.

Numbers don't lie. Except when it comes to weight loss. For years, dietitians swore weight management boiled down to one simple equation: Eat less, lose more.

Sounds logical. But today, we know that dropping pounds isn't just about mathematics. If it were, we wouldn't still be searching for the latest weight-loss miracle (and spending a collective $62 billion a year in the process). Why is weight loss such a challenge? One big reason is your hormones.

Our bodies are evolutionarily hard-wired to hang onto fat to protect against starvation and famine. So even though you might want to lose weight quickly, your body has other plans entirely. And it really doesn't matter which diet you choose. Whether it's keto, paleo, intermittent fasting or old-school calorie-cutting, rapid weight loss sets off alarm bells telling your body to restore the status quo—pronto. As soon as it gets the SOS, your body springs into action, releasing a flurry of hormones designed to put the pounds back on. Next thing you know, the weight you worked so hard to shed starts making a comeback.

But it doesn't have to be that way. By understanding how weight-loss hormones work, you can develop strategies to work around them and keep the pounds off for good. Here are five common hormone-driven changes that happen when you lose weight, plus one straightforward strategy to outsmart them.

1. You can't stop thinking about food

Feeling hungry? Blame it on ghrelin, a hormone made in your stomach. Ghrelin's job is to ensure that your body has a steady supply of energy on tap. It kicks in when you haven't eaten for a while, sending hunger signals from your gut to your brain telling you to start thinking about your next meal. Trouble is, ghrelin doesn't just rise when your belly is empty. It also spikes when you drop pounds, leading to a gnawing hunger that makes it nearly impossible to maintain your new weight.

2. Once you start eating, it's hard to stop

If ghrelin makes you hungry, then leptin is all about feeling full. Leptin is produced in your fat cells, and its mission is also energy preservation. When you have sufficient fat, you generate lots of leptin. So, you're easily satisfied, and everyone's happy. But when fat starts to dwindle, leptin follows, making it hard to know when to put down the fork.

3. You might want to eat more often

Know how slowly digested nutrients like protein and fiber keep your belly full between meals? There's a hormone in your small intestine, called cholecystokinin (CCK), that does the same thing. CCK works by reducing the rate at which food empties from your stomach. Unless you start losing weight, that is. Then CCK begins to tank. In one study, the longer volunteers dieted, the more their CCK levels dipped.

4. Your metabolism slows down

Hormones aren't just about appetite. They also influence your calorie burn. Take leptin, for example. In addition to helping you eat less, leptin also keeps your thyroid—and therefore your metabolism—in top shape. But when leptin drops after weight loss, metabolism often slows too, meaning you'll have to eat less just to maintain your new weight.

5. Your belly could get bigger

It's the ultimate paradox. Stress makes us want to eat more. At the same time, dieting is stressful. And that may have some unintended consequences—like belly fat. Several studies have found that diets (especially fasting plans) raise cortisol, a stress hormone that directs fat to your tummy. If that weren't enough, high cortisol levels also break down calorie-burning muscle, adding another hit to your metabolism.

Does anything good happen?

Despite these changes, weight loss isn't all bad news for your hormones. Some hormones improve after weight loss, doing good things for your health.

For instance, losing weight may:

  • Lower estrogen, which can protect from breast cancer.
  • Boost testosterone, helping to maintain muscle mass and bone density. It can also improve sex drive in all genders and increase sperm count if a person has testes and is not on androgen blockers.
  • Improve insulin sensitivity, reducing the risk of type 2 diabetes (or helping people living with type 2 better manage blood sugar).

So, how can you go about losing weight without all the hormone trouble?

So, how do you leverage the benefits of certain hormones while minimizing the downside of others? As a registered dietitian, I'm a big fan of a balanced diet rich in whole, minimally processed foods (the Mediterranean and DASH plans are two great examples). This way of eating is naturally filling, so you're less likely to struggle with post-diet rebound hunger. And it's easy to sustain long term, since it doesn't suggest restricting any one food—even sweet treats are on the menu, when enjoyed in moderation.

True, the weight won't melt off in a hurry. Instead, something even better will happen. You'll shed pounds slowly, giving your hormones a chance to adjust to your new weight rather than shocking them into chaos.

Bottom line

Research tells us that restrictive fad diets don't work when it comes to weight loss. In fact, they inevitably make the weight-loss process harder by sending your body—particularly your hormones—into protection mode. While it may seem tempting to hop on the latest trend for intermittent fasting or the keto diet, you're much better off following an eating pattern that will leave you feeling good at the end of each day—not deprived—and that's backed by research for its ability to help you lose weight and keep it off in the long run. The Mediterranean and DASH diets are two of the best options to help you live a healthier, more delicious life.

We at EatingWell understand that most studies, including the ones we reference in this article, are based on what happens to hormone levels in cisgender people whose gender aligns with the one assigned to them at birth. This is especially true when referring to sex hormones. We adjusted our language to be sure to include all identities but recognize that based on a person's use of gender-affirming puberty blockers or hormone therapy, some of this information may not apply to transgender and nonbinary individuals in the most comprehensive way it should. We also recognize that not all transgender and nonbinary people use hormones as part of their care.