Where does our fat go when we exercise? - CrowdScience podcast, BBC World Service

If, like CrowdScience listener Lili, you enjoy working out in the gym, you may have wondered where your fat disappears to when you exercise?

The short answer is that we convert it to energy that powers a whole range of physical processes, from breathing to walking as well as lying down and doing nothing. But the science behind energy expenditure is a little more complicated.

Presenter Anand Jagatia jumps on an exercise bike to have his metabolism measured and learns that he may be relying on an entirely different source of fuel as he works up a sweat.

Is all that hard work worth the effort it involves? Recent research suggests there is a limit to the number of calories humans can burn and that engaging in physical activity is not always a sure-fire way to keep trim.

So if working out is not the best way to lose weight, how about harnessing our own fat to tackle the complications of obesity? It used to be thought brown fat was exclusive to babies (and bears) but we now know adults have some of it too. Anand discovers that it appears to play a vital role in combatting a range of chronic diseases including hypertension and diabetes.

0:00 Introduction
1:19 CrowdScience listener Lili Clever wants to know: Where does fat go when we exercise?
2:54 What is fat aka adipose tissue?
4:15 Why it matters where fat is in your body
5:10 Male/female differences in fat tissue
6:25 Metabolism, fat and carbohydrates
9:43 Example of calorie expenditure
13:45 "We're breathing in other peoples atoms" at the gym
14:52 How fat use and storage changes as we get older
15:50 Our metabolism "stays pretty stable" during our adult lives
16:50 Does going to the gym a lot mean we burn more calories on average than someone living a more leisurely lifestyle?
19:40 Your relationship to food and weight loss/gain
20:45 "Obesity is a diet problem not an exercise problem"
21:30 White fat and brown fat
25:30 Summary and conclusion

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[English.moments_]

❤ When we exercise, our body uses stored energy in the form of glucose and fat to fuel our muscles. During exercise, our muscles break down these energy sources to produce ATP (adenosine triphosphate), which is the primary source of energy for our cells. As a result, glucose and fat are converted into carbon dioxide (which we exhale) and water (which we excrete through sweat and urine) as waste products. So essentially, the energy stored in our body is converted into heat, carbon dioxide, and water when we exercise.

[TT-fnxb]

Doing 5 hours of exercise a day and trying to keep a really low BMI sounds like a very difficult way to live.

[FriikD]

calorie deficit is the key in depleting fat cells, no matter what the studies say, this fact will never change. all exercise does is enable you to eat more, but you still have to figure out your metabolic rate and remain in a deficit if you wish to lose weight.

[felipearbustopotd]

09:51 we need oxygen to unlock the energy in fats or carbs.

The harder you push it, the more anaerobic you make the body, which will tip the scales into the body using glucose, but if you really want to burn FAT as a fuel source, then steady paced movement would suffice, walking at a pace or anything that enables you to breath through your nose would be ideal.

If you really dislike 'exercise' then eating low carb, and going to bed early can help. With less glucose roaming around and less glycogen in the muscle, the body will tap into fat stores quicker.

[kweuig]

5 hr a day exercise. Did I hear it right?

[regalherbsman]

This was such a fascinating clip. Subbed.

[duyenthanh]

This video opened my knowledge, thank you so much for this wonderful one. It’s the first time that I knew the fat works every time even when we speak, ...

[Pougie]

I wish they had spoken about gut microbiome. I've seen a case study where a mother got a fecal transfer from her daughter who was chubby, and this led the previously thin mother to gain weight she couldn't lose easily. There is some evidence to say the gut microbiome is a big part of weight distribution and loss/gain.

[rheung]

Our body fat came from carbohydrates, not the fat we ate, we delicate auto-balance of blood sugar and glycolysis biochemical reactions or so, is regulated by insulin among other biochemistry; and insulin resistance seems to be the early stage of diabetes. Personally, I changed diet by avoiding carb. in breakfast for 3 weeks, seems fixed by insulin resistance, characterised, among others, by often feeling tired just 2 hours after meal. Personally, I studied biochemistry in the university and yet so much more needs to be learnt and discovered. Eg the Alphafold breakthrough just last year.

[mcbrite]

I know that! I think it was 25% peed out, 75% breathed out? Maybe 1/3 to 2/3, it's been a while...

[LauraB.]

Carbohydrates are the only macronutrient not needed from food for survival. More and more people are putting the current theories to the test and determining carbs are not needed at all, even in athletics. There is a man who just ran five marathons in five days while fasting. He didn’t eat anything the whole five days. He used his body fat for fuel and made sure to drink enough water and get enough electrolytes. He didn’t hit the proverbial wall during this time either, as he was already fat adapted.

[mysteriousu]

Any exercise less than 30 mnts come under anaerobic exercise and your body solely depends on muscle glycogen for energy.

In the video, even though he was biking for 20 mnts, his body was using carbs primarily and he barely used fat.

In anaerobic exercise, your body doesn't depend on oxygen for the chemical reactions taking place in the body.

I do sprint and body uses the stored glycogen in the muscle to convert to cellular ATP.

10% of your glycogen that comes from carbs you eat, is stored in musles and the rest is stored as fat in liver for later use.

It takes some time for your body's liver to convert fat into glycogen. That's why when you do exercise longer than 20-30 mnts, your body needs oxygen to convert fat into fuel and you will start losing fat cells provided you are either eating less with no exercise or eating the same amount but doing exercise longer than 30 minutes.

Your brain alone consumes 30% of your intake. Your circulating blood glucose gets depleted in 45 mnts of idle sitting.

Liver is called the purification organ and its the main organ followed by kidneys that can convert fat to ATP your cells need. You don't want kidneys to do the job as it leads to keto acidosis producing ketones.

People who are on keto diet will suck at sprinting and marathoning because their carb intake is low which is needed for both in the initial phase.

I know some people who do heavy weights but can't do pushups. I don't care how much weight a person can lift if he or she can't lift her own body weight.

This video was very interesting wrt brown fat.

Thanks for sharing.

[LauraB.]

Why do we keep trying to sell exercise being important for fat loss? I’m not saying don’t exercise, and I’m not saying it doesn’t help a little, but the vast majority of fat loss is what you eat.

We have been lied to repeatedly about what to eat. First off, eat whole food, no processed food, grains, seed oils. Then, if you have metabolic issues (it’s estimated that 93% of American adults are metabolically unhealthy or have insulin resistance. Not sure about other countries), it means your body is becoming intolerant to carbohydrate, so the less carbohydrate you eat, the better. Then incorporate some fasting. It’s not always easy, but it is simple.

Insulin resistance causes all modern chronic disease including cancer, type 2, obesity, PCOS, autoimmune, heart disease, etc. And the vast majority of folks can improve symptoms, if not completely reverse insulin resistance, as well as obesity, HBP, high glucose, type 2, PCOS, autoimmune by eating fewer carbs less often.

If you want to add in exercise, go for it, BUT focus on food initially. Also, fat loss is mostly hormonal, not about calories. For those with metabolic issues, exercise without carbohydrate restriction will get you nowhere.

[weston.weston]

Exercise five hours a day? She must have a lot of extra time. I am physically active too, and I ❤ it but my work and other commitments don't allow me to work out five hours per day.

[shazanakhan]

Did she just say she exercise 5hrs a day? Theres something called having rest day and exhaustion. Thats alot of wear and tear to the joints and muscles. I wonder how long she can keeo up with those without getting arthritis, bones issues or hip, knee replacements. Being scared of obesity and damaging joints isnt tge way forward, having a balance with diet n exercise is key.

[FriikD]

obese Americans burning the same amount of calories a lean athlete does is nothing shocking. it's basic thermodynamics. if your organs have to work overtime to carry 100 extra pounds of fat, that takes more energy. that's also why obese people have a different bmi than a lean person. if you don't know anything about nutrition, which is the case for an overwhelming majority, then it's easy to over consume food, especially in the US where fast food and processed junk in general is so ingrained in culture.

[jstello]

If you don't measure the calories in a person's poop the concept of calories is absolutely meaningless. Everyone seems to miss this point, even Peter Attia. Also, what we call calories is not the energy in food. It's the energy it can release through combustion. Combustion is not digestion.

[Pougie]

@2:00 Did she just say she works out 5 hours every day???

[dominican]

Is the video incomplete and they just published it as is? Theres a layer missing: the actual video layer 😂😂😂

[lalonkarim]

The reason those Hadzas and Americans use the same number of calories even though they have very different activity levels is - the Americans are much heavier. Heavier people use more calories, even doing daily tasks.