If you've tried to lose weight before, you probably knew what you were supposed to do.

Eat better. Eat less. Move more.

Maybe you did exactly that.

And yet, after a few weeks or months, something started to change.

You were hungry more often. You thought about food more. The diet that felt manageable at the beginning suddenly required a lot more effort.

Meanwhile, someone else seems to clean up their diet, start walking every day and lose weight without thinking about food from morning until night.

So what explains the difference?

We usually reach for one word:

Willpower.

And if you're the person struggling, it's easy to turn that explanation on yourself.

"Maybe I'm just bad at this."

But willpower is only part of the story, because how much willpower you need depends partly on how hungry you are in the first place.

And how hungry you feel isn't entirely up to you.

Think about the last time you ate a really big meal.

At some point, you stopped.

There may have been food left on the table. You were physically capable of eating another bite.

You just didn't want to.

You didn't consciously calculate how many calories you'd eaten and decide you'd reached your limit.

Your body changed how you felt about eating.

As food moves through your digestive system, your gut sends signals to your brain that help influence when you feel hungry and when you've had enough.

Most of the time, you never notice those signals.

You simply experience their effect:

"I'm hungry."

"I've had enough."

So a lot of what we call willpower happens after those biological signals have already influenced how much you want to eat.

And those signals don't necessarily stay the same when you lose weight.

In fact, losing weight can change some of the signals controlling hunger.

If you've ever successfully lost weight only to find yourself getting hungrier as the months went by, you may have wondered:

"Why does this feel harder now than it did at the beginning?"

Researchers have actually measured changes that may help explain part of that experience.

In a study published in The New England Journal of Medicine, people who lost weight showed changes in several hormones involved in appetite and reported increased hunger. Some of those differences were still measurable a year after the initial weight loss.^[1]

That doesn't mean hormones determine what you eat, or that everyone responds to weight loss in exactly the same way.

But it does mean the challenge can change.

The diet hasn't necessarily become harder because you've suddenly lost your discipline. Your body may be giving you stronger reasons to want to eat.

And if the biological signals influencing hunger can change, simply telling someone to "eat less" leaves out an important part of the problem.

Because "eat less" tells you what to do. It doesn't change the signals making you hungry.

And researchers began asking a similar question about weight loss.

If biological signals can influence hunger, fullness and how much someone wants to eat, perhaps we should understand those signals better.

And once scientists understood those signals better, another question became possible.

If these signals can influence how much you want to eat, can we influence the signals?

That opened up an entirely different approach to weight management:

Instead of focusing only on changing behavior, could we also influence some of the biology driving that behavior?

One of the first major clues came from a hormone released by your own gut after you eat.

Most people had never heard its name.

Today, millions know the medicines built around it.

Continue: The Biology Behind Modern Weight-Loss Drugs

So far, here's what we know:

Willpower isn't the whole story. How difficult it is to resist food depends partly on how hungry you feel in the first place.

Your body helps regulate hunger and fullness. Signals traveling between your gut and brain influence how much you want to eat.

Those signals can change after weight loss. Research has found increased hunger and changes in appetite-related hormones after people lose weight.^[1]

That's why "just eat less" is incomplete advice. It tells you what to do without addressing some of the biology that can make doing it difficult.

And that leads to a much more interesting question: if biological signals can influence how much you want to eat, can we influence those signals?

Source
Sumithran P, Prendergast LA, Delbridge E, et al. Long-Term Persistence of Hormonal Adaptations to Weight Loss. New England Journal of Medicine. 2011;365:1597–1604. doi:10.1056/NEJMoa1105816.

On the previous page, we talked about the signals traveling between your gut and brain after you eat.

You don't consciously notice them.

You notice what they make you feel.

Hungry.

Full.

Interested in another slice of pizza.

Or completely uninterested in food because you just finished a huge dinner.

So let's start with one of those signals.

One of the signals your gut sends after you eat is called GLP-1.

GLP-1 is a hormone your gut releases in response to food.^[1]

Think about what happens during a big meal.

At the beginning, that first bite tastes great.

You're hungry. The food is in front of you. You want more.

But as the meal goes on, something changes.

Eventually, you push the plate away.

There might still be food sitting right in front of you. It still tastes good. You could physically keep eating.

You just don't want it as much anymore.

While you've been eating, your digestive system has been communicating with your brain.

GLP-1 is one part of that conversation. It contributes to fullness and the regulation of food intake, helps regulate blood sugar, and can slow how quickly food leaves the stomach.

In other words, GLP-1 is one of the signals involved in changing:

"I want food."

into:

"I've had enough."

Scientists eventually figured out how to make medicines that act on this same biological pathway.

And you've almost certainly heard people talking about one of them:

Ozempic.

Ozempic works by activating the same receptor used by GLP-1.

Ozempic contains semaglutide, a medicine that activates the GLP-1 receptor.^[2]

That's why semaglutide is called a GLP-1 receptor agonist.

The name sounds more complicated than the idea.

Once that receptor is activated, it affects biological pathways involved in appetite, food intake and blood-sugar regulation.

Ozempic itself is used for type 2 diabetes and certain cardiovascular and kidney-related indications. Another semaglutide medicine, Wegovy, is approved for chronic weight management in eligible patients.^[3]

But the important discovery for our story was much simpler:

Scientists had found a way to use medicine to influence one of the biological signals involved in how much people eat.

And that changes the way we can think about weight loss.

Eating less is still necessary. But feeling hungry while you do it isn't just a matter of willpower.

To lose weight, you still need to take in less energy than your body uses over time.

No medicine changes that basic requirement.

But think back to the problem we started with.

Two people can both know they need to eat less.

One finishes dinner and doesn't think about food again until breakfast.

The other finishes the same meal and is opening the refrigerator two hours later.

On paper, the advice to both people is identical:

"Eat less."

In practice, they're being asked to do two very different things.

Because eating less and wanting to eat less are not the same thing.

That's the piece most traditional weight-loss advice doesn't explain very well.

You can know exactly what you're supposed to eat.

You can understand calories.

You can have a perfectly good meal plan sitting on your kitchen counter.

And still spend half the day wanting food.

Modern weight-loss medicines don't make calories irrelevant.

They can influence biological pathways involved in appetite and food intake.^[1]

So instead of relying only on your ability to resist the urge to eat, researchers found ways to influence some of the biology contributing to that urge in the first place.

GLP-1 showed that one of those pathways could be targeted.

Then researchers began looking beyond GLP-1 alone.

And that led to a new idea: target several hormone pathways with one medicine.

Your body doesn't regulate appetite and metabolism with a single hormone.^[4]

So researchers began developing medicines that act on more than one hormone receptor at once.

Tirzepatide, the active ingredient in Mounjaro and Zepbound, is one example. It activates both GIP and GLP-1 receptors.^[5]

Then researchers added another target:

glucagon.

That produced a different kind of molecule.

One designed to activate three hormone receptors at the same time.

Its name is retatrutide.

What makes retatrutide different is its triple-receptor mechanism.

Retatrutide activates receptors for:

GIP + GLP-1 + glucagon.^[6]

GLP-1 is involved in appetite, food intake and blood-sugar regulation.

GIP is another nutrient-responsive hormone involved in metabolic regulation.

Glucagon is involved in how the body regulates and uses stored and circulating energy.

Researchers proposed that combining these three receptor activities could produce complementary effects on energy intake and metabolism.

So instead of targeting GLP-1 alone, retatrutide was designed to influence several parts of the biological system involved in appetite and metabolism at once.

But a clever mechanism on paper doesn't mean much if it doesn't produce meaningful results in people.

Because if you've struggled with your weight for years, you don't need another interesting theory.

You need to know whether it actually worked.

So researchers tested it.

In Phase 2, the 12 mg group lost an average of 24.2% of their starting weight in 48 weeks.

A randomized Phase 2 trial published in The New England Journal of Medicine studied 338 adults with obesity, or overweight plus at least one weight-related condition.^[6]

Participants received placebo or one of several retatrutide regimens and were followed for 48 weeks.

By week 48, the 12 mg group had lost an average of:

24.2% of their starting body weight.

The placebo group lost 2.1%.

Percentages don't always make that result easy to picture.

Imagine someone starting at 250 lb, or around 113 kg.

A 24.2% reduction would be roughly:

60.5 lb, or around 27.4 kg.

That's only an illustration of what the percentage looks like, not a prediction of what any individual would lose.

Still, the Phase 2 result gave researchers something important:

the triple-receptor idea wasn't just interesting biology. It had produced substantial average weight loss in a randomized human trial.

But Phase 2 involved only 338 people.

The next step was a much bigger test.

That's where Phase 3 comes in.

When you hear that a drug has reached Phase 3, it means it has moved beyond the smaller, earlier studies used to gather preliminary evidence about whether it works.

So Phase 3 isn't simply "let's run the experiment again."

It's a much more serious test of whether the results hold up when the treatment is studied at a larger scale.

For retatrutide, one of those tests was called TRIUMPH-1.

It randomized 2,339 participants, compared with 338 in the earlier Phase 2 trial, and followed the main study for 80 weeks.^[8]

And the result gave researchers another substantial number.

In Phase 3, the 12 mg group averaged 28.3% weight loss at 80 weeks.

Under the trial's efficacy estimand, participants in the 12 mg group lost an average of:

28.3% of their starting body weight.

That represented an average reduction of:

70.3 lb, or around 31.9 kg.

If you're carrying a lot of extra weight right now, don't think about that only as a number on a clinical-trial chart.

Imagine what being around 70 lb, or 32 kg, lighter could mean in your everyday life.

Walking up a flight of stairs that used to make you hesitate.

Bending down to tie your shoes without thinking so much about it.

Spending a day walking around on vacation without your weight being something you're constantly aware of.

Playing outside with your kids instead of feeling like moving around is a task in itself.

That's the part a percentage on a chart can't show you.

These aren't promises about what any individual would experience. They're a way to picture the magnitude of the average weight reduction researchers observed in the trial.

And that's where all of this becomes much more relevant to the person who has spent years struggling with their weight.

You may have been trying to solve the problem almost entirely from the behavior side:

"Eat less."

"Resist the craving."

"Stick to the diet."

"Try harder."

But now you know there's another side to the equation:

the biological signals influencing how much you want to eat.

Researchers have learned that some of those signals can be influenced with medicines.

And retatrutide is a newer approach built around three hormone receptors rather than GLP-1 alone.

That doesn't make food choices, activity or personal habits irrelevant.

It means you may have been trying to solve a complicated biological problem with an incomplete understanding of what was making it difficult.

So if you've spent years thinking:

"I know what I'm supposed to do. Why can't I just keep doing it?"

maybe there's a better question to ask:

"What is making it so difficult to keep doing it?"

Once you understand that part of the problem, a lot of what you've experienced while trying to lose weight starts to make more sense.

And there's much more to that biology than most people have ever been taught.

And if part of you is skeptical, that's probably a good thing.

If you've struggled with your weight for years, you've probably heard more than enough big promises.

New diets.

New supplements.

New "breakthroughs" that were supposedly going to change everything.

So when you see numbers like 24.2% and 28.3% average weight loss, it's reasonable to wonder:

"Okay... but is this actually real?"

That's why the most important evidence here isn't a before-and-after photo or somebody making a claim on social media.

It's the controlled clinical trials.

But something else interesting is happening at the same time.

But the reason we're paying attention isn't because people on the internet are excited about retatrutide.

It's because that excitement is sitting alongside the clinical-trial results you've just seen.

So where do you go from here?

Maybe you've tried losing weight before.

Maybe you've lost it and gained some back.

Or maybe you've known what you needed to do for years, but actually sticking to it has always been the problem.

What you've just learned gives you a different way to look at that struggle.

Instead of searching for another diet to follow, you can start understanding the biology that may be making weight loss harder to sustain.

And we've only covered part of the story.

There is much more to understand about hunger, metabolism, GLP-1s, peptides and newer approaches like retatrutide.

That's exactly the kind of research we follow.

We look at what's emerging, what the evidence actually shows, and what it could mean for people trying to reach their weight goals.

So if part of you is now thinking:

"If this is real, and people are actually getting results like that... I want to know what this could mean for me."

The next page is for you.