Why It's So Hard to Lose Weight According to Science

Summary

The video script explores the biological challenges of weight loss, explaining how the body resists shedding fat due to hormonal changes. Leptin, produced by fat cells, signals starvation when levels drop, prompting the brain to conserve energy and increase hunger. Ghrelin levels rise, and insulin and amylin levels fall, further boosting appetite. The body becomes more energy-efficient, and even after weight is regained, the metabolic rate remains lower, making it harder to maintain weight loss. The script highlights the complexity of weight management and the ongoing research into individual responses to dieting.

Takeaways

• 🏋️ Losing weight is challenging due to the body's resistance to losing its energy buffer, which includes stored fat.
• 🍕 The body's fat cells are a survival advantage, providing a rich energy source for times of need.
• 🔄 The body's hormonal response to weight loss includes a decrease in leptin levels, which can trigger starvation signals and increased appetite.
• 🧠 The hypothalamus interprets lower leptin levels as a sign of starvation and instructs the body to conserve energy and increase food intake.
• 📈 Ghrelin levels rise when calories are restricted, signaling the brain to increase appetite and make individuals feel hungrier.
• 🍽 The body becomes more energy-efficient during weight loss, with muscles shifting their primary fuel source from fat to glucose.
• 🔄 Hormonal changes persist even after weight loss efforts cease, leading to a continued state of perceived starvation and energy conservation.
• 🔄 Regaining weight does not reset the body's energy-efficient mode, potentially leading to future weight gain.
• 🔍 A 2016 study showed that weight loss contestants experienced a persistent decrease in their resting metabolic rates, even after regaining weight.
• 🔢 The body's resting metabolic rate, or the calories burned at rest, is a crucial measure of energy expenditure and can be significantly impacted by weight loss and gain.
• 🧬 Individual responses to weight loss vary, and ongoing research is exploring the influence of genetics, diet, and other factors on this process.

Q & A

Why is losing weight often difficult for most people?

Losing weight is difficult because the body resists weight loss as a means of preserving its energy buffer. This resistance is partly due to hormonal changes that occur when calorie intake is reduced.

What is the role of adipose tissue in the body's energy storage and utilization?

Adipose tissue stores fat, which is a highly energy-rich substance. The body can use this fat to fuel its cells in times of need, such as when food is scarce or during growth and reproduction.

What is leptin and how does it affect weight loss efforts?

Leptin is a hormone secreted by fat cells. Larger fat cells produce more leptin. When weight is lost, leptin levels drop, which can signal the brain to conserve energy and increase appetite to rebuild energy reserves.

How does the hormone ghrelin influence appetite during weight loss attempts?

Ghrelin is a hormone that increases when the stomach is not being filled. Higher levels of ghrelin signal the brain to increase appetite, making individuals feel hungrier.

What are the effects of reduced insulin and amylin levels on the body during calorie restriction?

Reduced insulin and amylin levels, which are important for regulating blood sugar and signaling fullness, can lead the brain to perceive a state of starvation, further increasing appetite.

How does the brain respond to hormonal changes during dieting?

The brain may become more aware of the food that is being restricted and increase the pleasure felt when consuming it. This can make it harder to resist overeating.

How does the body become more energy-efficient during weight loss?

The body, including muscles and other tissues, makes small changes to become more efficient, such as muscles relying more on glucose for energy instead of stored fat during calorie restriction.

Why does the hormonal starvation signal persist even after stopping a diet?

The hormonal starvation signal persists because some hormones, like leptin, are based on the amount of fat and may not immediately adjust back to normal levels even after a diet is stopped.

What was the finding of the 2016 study that followed contestants from a weight loss competition?

The study found that after losing weight, the contestants' resting metabolic rates dropped significantly and did not return to normal even after they regained some of the weight, leading to a continued state of energy conservation.

How does the body's energy usage change after weight loss and regain?

After weight loss and regain, the body continues to use fewer calories per kilogram than similarly sized individuals who have not experienced weight fluctuations, making it easier to gain weight back.

What factors are scientists investigating to understand individual differences in body resistance to weight loss?

Scientists are looking into genetics, dietary habits, and other factors to understand why different people experience varying degrees of resistance to weight loss.

Outlines

00:00

🏋️‍♂️ The Struggle of Weight Loss

Weight loss is a challenging process that often results in failure due to the body's resistance to losing its energy reserves. The body's adipose tissue stores fat, which is an energy-rich substance. When calorie intake is reduced, hormonal changes occur, such as a decrease in leptin levels, leading the brain to signal for energy conservation and increased appetite. Ghrelin levels rise, promoting hunger, while insulin and amylin levels drop, signaling a need for more food. The body also becomes more energy-efficient, with muscles shifting their fuel source from fat to glucose. These hormonal changes can persist even after dieting ends, making it difficult to maintain weight loss and causing the body to act as if it's still being starved.

🔬 Hormonal Impact on Weight Loss

This paragraph delves into the hormonal responses that make weight loss difficult. The body's hormonal signals interpret a decrease in leptin, due to fat loss, as a sign of starvation, prompting the hypothalamus to conserve energy and increase appetite. Other hormones like ghrelin, insulin, and amylin also play roles in signaling hunger and fullness. The brain heightens awareness of food and the pleasure derived from eating when dieting, making it harder to resist temptation. The body's tissues, including muscles, adapt to become more energy-efficient, which can hinder weight loss efforts.

🔄 Long-Term Effects of Dieting on Hormones and Metabolism

The hormonal starvation signals initiated by dieting do not cease post-diet, affecting leptin levels based on fat mass and other hormones that may remain altered for years. This can cause the body to continue acting as if starved even after normal eating is resumed. A study on contestants from a weight loss competition showed that after significant weight loss, their resting metabolic rates dropped and did not recover even when weight was regained. This resulted in a persistently lower calorie burn rate, making future weight loss attempts even more challenging.

📉 The Complexity of Post-Weight Loss Metabolism

The relationship between body weight and energy expenditure is not linear. Individuals who have experienced weight fluctuations use fewer calories per kilogram than those whose weight has remained stable. This is evident in the study of weight loss competition contestants, who, despite regaining weight, continued to burn fewer calories than expected for their final weights. The duration of these anti-weight-loss changes is unclear, and the body's resistance to weight loss varies among individuals, influenced by genetics, diet, and other factors.

Keywords

💡Weight Loss

Weight loss refers to the process of reducing body mass, typically through a combination of diet and exercise. In the video, weight loss is depicted as a challenging endeavor due to the body's resistance to losing its energy reserves, highlighting the difficulty in maintaining a reduced body size.

💡Adipose Tissue

Adipose tissue is specialized connective tissue that stores energy in the form of fat. The script explains that the body uses fat stored in adipose tissue as a backup energy source, which is why having some fat is beneficial from a survival perspective, but also why the body resists losing it during weight loss.

💡Leptin

Leptin is a hormone produced by fat cells that helps regulate appetite and energy balance. The video script describes how leptin levels drop when weight is lost, signaling the brain to conserve energy and increase appetite, thereby making weight loss more difficult.

💡Hormonal Changes

Hormonal changes refer to shifts in hormone levels in response to various stimuli, such as weight loss. The script discusses how the body's hormonal response to dieting can increase hunger and cravings, and make the body more energy-efficient, all of which work against weight loss efforts.

💡Ghrelin

Ghrelin is a hormone that stimulates appetite. The script mentions that when calorie intake is reduced, ghrelin levels rise, signaling the brain to increase appetite, which can make it harder to stick to a diet.

💡Insulin and Amylin

Insulin and amylin are hormones that regulate blood sugar and signal fullness, respectively. The video explains that when dieting, the pancreas secretes less insulin and amylin, which can lead to increased hunger and a greater desire to eat.

💡Energy Efficiency

Energy efficiency in the context of the body refers to the metabolic adjustments that occur to conserve energy. The script describes how the body becomes more energy-efficient during weight loss, including changes in muscle fuel sources and other tissue adjustments, making it harder to continue losing weight.

💡Starvation Signal

A starvation signal is a hormonal cue that the body interprets as a lack of food intake. The video script explains that even after weight loss, the body may continue to send starvation signals, leading to a persistent state of energy conservation and increased appetite.

💡Resting Metabolic Rate

Resting metabolic rate (RMR) is the number of calories the body burns at rest to maintain basic physiological functions. The script cites a study where contestants who lost weight had a significantly reduced RMR, which did not return to normal even after regaining weight, making future weight loss attempts more challenging.

💡Body's Resistance

The body's resistance refers to the physiological and hormonal reactions that oppose weight loss. The video emphasizes that the body fights against slimming down fiercely, which is why many people struggle with maintaining weight loss.

💡Genetics

Genetics refers to the hereditary factors that influence an individual's traits, including their response to weight loss. The script suggests that scientists are investigating how genetics, along with other factors like diet, affect the body's resistance to weight loss.

Highlights

Losing weight is a challenging process as most people who attempt it do not succeed or end up regaining the weight.

The body resists weight loss due to the high energy content of stored fat, which is beneficial for survival.

Weight loss is not as simple as eating less and forcing the body to use fat, as the body reacts to conserve energy.

Hormonal changes, such as a decrease in leptin levels, cause the brain to interpret weight loss as starvation and promote energy conservation.

Other hormones like ghrelin, insulin, and amylin play a role in signaling hunger and fullness, affecting appetite during calorie restriction.

The brain responds to hormonal changes by increasing awareness of food and enhancing the pleasure of eating, making it harder to resist food.

The body becomes more energy-efficient during weight loss, with muscles changing their fuel sources to rely more on glucose.

Hormonal starvation signals persist even after dieting stops, causing the body to continue acting as if it is being starved.

Weight regain does not shift the body out of its energy-efficient mode, leading to a slower metabolism even at a higher weight.

A study followed weight loss contestants and found that their resting metabolic rates dropped significantly and did not return to normal after weight regain.

People who have lost and regained weight use fewer calories per kilogram than those whose weight has not changed.

The duration of anti-weight-loss changes in the body is unclear, and they may never completely disappear.

Individual differences in the body's resistance to weight loss are influenced by genetics, diet, and other factors.

The fierce resistance of the body to weight loss is a significant reason why many people struggle with maintaining weight loss.

SciShow's educational content is supported by patrons on Patreon, who enable the creation of informative videos.

Transcripts

[ ♪INTRO ]

Losing weight is hard.

Like, really, really, really hard.

The overwhelming majority of people who try to do it don’t succeed or end up gaining

back what they lose, sometimes more.

And that’s not just because pizza is amazing.

It turns out your body actually pushes back when you attempt to slim down.

The fat stored in your adipose tissue is a super energy-rich substance that your body

can use in a pinch to fuel your cells.

If you can’t eat for whatever reason, or need a little extra energy to grow or reproduce,

your body can turn to your fat — which is why, from a survival perspective, having some

fat is actually a good thing!

Still, you’d think that losing weight would be pretty straightforward: just eat less than

you need, force your body use up some of its fat, then go back to eating a normal amount

when you’re the size you want to be.

But the body doesn’t want to lose its energy buffer — no matter how large or small it

is — so when you cut calories, it reacts in ways that ultimately make it harder to

lose weight.

A lot of the push back is driven by changes to hormones.

One of the most important is leptin, a hormone secreted by your fat cells.

The larger your fat cells are, the more leptin they produce.

So when you lose weight, leptin levels drop.

Parts of your brain like your hypothalamus interpret less leptin as starvation, and it

jumps in and starts telling your body to conserve energy and to eat more to rebuild those reserves.

Other organs also use hormones to complain to your brain about the decrease in fuel intake.

Your stomach tells your brain it’s not getting filled by increasing levels of the hormone

ghrelin.

At the same time, your pancreas secretes less insulin, which regulates blood sugar, and

amylin, which signals fullness.

So when you cut calories, ghrelin levels rise and insulin and amylin levels plummet, signalling

your brain to increase appetite — making you feel ravenous.

In addition to changing how hungry you feel, a suite of studies have suggested your brain

responds to these hormonal changes by making you more aware of all the food you’re not

eating, and upping the pleasure you feel if you do cave in.

Meanwhile, the rest of your body becomes more energy-efficient.

For example, your muscles change where they get their fuel.

When your muscles need energy, they generally use a mix of stored fat and circulating glucose.

But when you’re on a calorie-restricted diet, they rely more heavily on glucose, so

they end up pulling more energy from the foods you eat instead of those fat stores you’re

trying to lose.

They also make other small changes to become more efficient — and so do other tissues

in your body.

Here’s the really annoying thing: this hormonal starvation signal doesn’t stop when you

stop dieting.

That makes sense for leptin, since it’s based on the amount of fat you have.

But other hormones which generally respond to food intake can stay on that slower production

cycle even when you return to normal eating.

And these hormones can stay altered for years.

So even when you’ve stopped restricting calories, your body continues to act like

it’s being starved — which is a big part of why people who lose weight often gain it

back.

To make matters worse, even regaining the weight doesn’t shift your body out of energy-efficient

mode.

In general, the smaller you are, the less energy you need to fuel everything.

But it’s not a simple, linear relationship.

How much energy you use per kilo at any given body weight varies depending on whether you’ve

ever been heavier or skinnier.

And this effect could be clearly seen in a 2016 study which followed contestants from

a televised weight loss competition for six years.

In particular, the researchers looked at the participants’ resting metabolic rates: the

calories their bodies burned at rest.

It’s basically a measure of the minimum amount of energy needed to keep a person’s

cells running.

After the 30 week contest, the 14 participants lost an average of about 58 kilograms, and

their resting metabolic rates dropped by about 610 calories per day.

In the years that followed, though, they gained back an average of 41 kilos, and their metabolic

rates didn’t go back up accordingly.

They ended up burning 500 calories a day less than they should have at their final weights.

Which means to lose weight in the future, they’d have to restrict themselves even

more than they did the first time around.

Lots of other studies have come to similar conclusions.

After people lose weight, even if they gain it back, their bodies simply use fewer calories

per kilogram than similarly sized people whose weight hasn’t changed.

And that means they have to eat less to stay at that weight than people who were never

heavier, and they gain weight faster if they do overeat.

It’s not yet clear just how long all these anti-weight-loss changes last — or if they

ever completely go away.

But not everyone experiences the same degree of resistance from their bodies.

Scientists are still trying to figure out how our person’s genetics, the foods they

eat, and other factors affect how a person responds to dieting.

But given how fiercely the body can fight slimming down, it’s no wonder so many people

struggle with it.

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[ ♪ OUTRO ]