Can anybody give me a good explanation as to how exercise helps one lose weight?

Earlier this year I decided to resume working out. On account of my blindness I can’t run or bike outside much anymore, so instead I joined Planet Fitness. It has been working (I have shed 8 pounds since February 1), sparking a debate among certain persons as to the cause. @Least one person, adding up the number of calories each session on the exercise bike is elected to burn, says that I am going to the gym for no reason, that it must be a change in eating habits. I don’t think this is true; my eating habits haven’t really changed all that much. True, I do have mostly salad for dinner, but that was already so.

So can someone give a good explanation for the non–medical/non-biologist of the mechanism involved in exercise-related weight loss?

There are several mechanisms.

  1. The exercise itself burns more calories than you would otherwise.
  2. Exercise increases muscle mass. That process requires calories.
  3. Increased muscle mass burns calories due to the muscles needing energy, even when not doing very much work.
  4. Exercise changes behavior, which often leads to healthier eating habits.

No idea about your question, but welcome back, Skald!

Your body really only knows how to do a few things, mainly “survive”, “reproduce”, and “do stuff.” Whatever you’re doing that counts as exercise is “stuff.” Since your body is lazy, the first thing it’s going to do when you start to exercise is punish you by hurting a lot, so maybe you don’t do that stuff any more. Silly human. If you keep going back to the gym and exercising, your body thinks “well, crap, that didn’t work; how do we keep this from being a pain in the neck?” So your body starts to change itself so that it can do the exercise more easily: if you’re lifting weights, it gets stronger. If you’re running, you get more aerobic and lose upper body mass. If you’re swimming, you retain a bit of fat all over your body, both for flotation and for insulation. Some people who start to exercise heavily, even though they look and feel better, and they might even be getting thinner, will actually gain weight, because muscle is denser than fat.

Calories are a unit of energy.

Your body requires energy to operate (as does anything). We measure those units in Kcals (Kilo Calories or 1000 calories) but often just shortened to calories when talking about food.

So, you eat food which adds to the gas tank that is calories. Your body burns those calories to operate. Leftover calories are either stored (usually as fat but can also be made into things like muscle) or expelled (pooping).

At the end of the day the best diet is merely calories in, calories out. If you eat fewer calories than you burn you lose weight. If you eat more calories than you burn you gain weight.

Exercise makes you burn more fuel same as stepping on the gas pedal of a car causes it to burn more fuel.

In some extreme cases like Olympic athletes they can eat a ridiculous amount of food (the Olympic swimmer Michael Phelps reportedly ate over 8000 calories a day) and be in tip-top shape but if you are (say) swimming several miles a day at top speed you need it…just like gas in a race car.

Ignore fad diets. It is really just calories in, calories out to lose/gain weight.

I am not on any sort of formal diet at all. And my intention wasn’t really to lose weight. I would like to reduce my waist size a couple of inches and to have a healthier heart, so the weight loss is, while not unexpected, not the primary goal.

Moderate exercise is very healthy and worthwhile. No need to go crazy about it to get a lot of health benefits.

Run, bike, swim, climb some stairs…lots of things you can do. Even a good long walk is worthwhile.

You may or may not lose weight but if that is not a goal no worries (actually exercise is not all that great at burning weight unless you exercise a LOT…still very healthy even with moderate exercise though).

This is rather an anthropomorphic view of the human body, attributing motivation to internal systems that are themselves not sapient. So initial pain from exercise is not motivated by anything, it is a biochemical reaction to stress. Improvements in physiology after exercise are likewise not motivated by anything, they are bio-mechanical reactions to stress. The key is to give them the right stress and not too much of it.

This has been your pedantic treat for the week, offered in the spirit of preventing sloppy thinking in areas where it can do real damage (not this area, so much).

For the OP’s question, I think **beowulff **has the meat of it down pretty concisely.

Not necessarily. Exercise does not necessarily lead to more muscle mass.

My GF exercises religiously. She does not gain muscle mass. In fact she does not gain any mass.

Her exercise is allowing her to keep her existing muscle mass.
Without it, she would lose muscle.

Welcome back, Skald!!!

Now that I have that off my chest, resistance training burns off some calories, and it increases muscle mass. More in men than women - women don’t have the testosterone levels to build much muscle mass, with fairly rare exceptions.

Muscle needs more energy to maintain itself. Muscles are in a constant state of weak contraction, where only a few fibers are contracting. This is what we think of as “muscle tone”. Fat cells don’t have this, so they don’t use up as much energy. If you increase your muscle mass, you are raising your metabolic rate and thus burn more calories even at rest. Muscle also breaks down during exercise, and it takes a certain amount of calories to rebuild them back to baseline, and then to improve so as to compensate for the homeostatic disruption of exercise and prepare for the next overload.

Building muscle also helps your circulation, because contracting muscles squeeze the blood vessels and push blood thru the veins back to the heart. They also become more vascularized to supply a greater blood supply for future overloads.


PS - Welcome back, Skald!!!

This bears repeating. People will swear that losing weight is 90% diet or some such nonsense. When I used to try to watch my diet without exercising (or only exercising minimally), it was a losing battle. I did the best I could based on the conflicting research I read, and even in my confusion it was a constant game of willpower.

When I began to work out intensely and regularly, I could sense exactly what nutrients my body needed, and while it still took willpower, it didn’t take nearly as much. Yes, you do have to be careful not to overeat, but it is so much easier to eat fresh produce and whole, unprocessed foods when you legitimately crave them.

Welcome back Skald.

I read this CNN article yesterday.

Exercising uses energy, and you exhale more.

Perhaps that explains why I am still full of shit.

I’ve been wondering, what mechanism in the body “grabs” the fat cell from my belly (blood stream, I guess) and “converts” it?

I agree that exercise can change how you look at food. It’s like there is symbiotic relationship between working out and eating right. I know that’s true for me. When I workout regularly, I naturally make better and healthier food choices. If I’m not working out, then all the bad foods seem much more desirable. But I think that’s triggered when working out intensely. Mild workouts (like a short walk) don’t have the same effect. But with an hour+ of cardio, it’s much easier for me to eat right.

So part of it is that the exercise is burning some calories, but another part is that the exercise is helping to diminish cravings for bad foods and increase those for good foods.

If I understand your question, here you go.


Yes, perfect. Thank you.

Have you considered something like Achilles T C or CAF? I’ve seen blind runners racing by holding a short rope tied to a ‘seeing-eye’ runner & know of a group that does cycling for blind runners by making them a stoker (rear seat) on a tandem bike. The pilot brings their tandem, so you don’t even need to buy a bike.

I hate the gym & would rather be outside; the above gives you some of those options, safely.

This is not quite true. Calories are a measure of the energetic yield from a food (or rather the sugars, fats, and proteins that comprise it) as measured by heating them to dissociation in a bomb calorimeter. It should go without saying that your body is not a bomb calorimeter and your metabolism does not simply burn food for thermal energy. Calories should therefore be taken as a general guide to how much energy foods contain but does not necessarily reflect the propensity of any particular food to spike blood sugar or encourage fat production and deposition. Also, dietary fat does not create subcutaneous or visceral fat, and dietary cholesteral does not create cholesterol within the body; both provide constituants for fats and sterols but are broken down by the metabolism first into basic compounds and amino acids.

Agree with ignoring fad diets; a diet specifically for reducing obesity (produced by a registered dietician for a specific end goal) might be low in carbohydrates and relatively high in proteins and fats, but a general diet should be about 50:30:20 or 55:25:20 in carbohydrates:fats:proteins, with foods that have a generally low glycemic index, a decent amount of dietary fiber for regularity, and plenty of leafy green vegetables and a variety of fresh fruits for micronutrients (vitamins) which can be absorbed in a highly bioavailable manner. Any diet that includes a source of complete proteins, grains or low GI carbs, and plenty of fresh fruits and vegetables will serve and unless you have some specific nutritional deficiency or metabolic syndrome supplementation with vitamins is not really necessary. Also, a diet with a lot of low-glucose vegetable matter and the appropriate amount of fats will make you feel satiated (full) without overeating and without having to count calories. Eating a diet of fast food or highly processed ‘box’ food with high carbohydrate load will cause you to overeat by design. As Eat. Move. Improve. advises:

*Really though, keep it simple. There’s lots of good sayings that are generally true:

Eat real food
Avoid refined carbohydrates
Avoid things that come in a package
If your grandmother wouldn’t recognize it don’t eat it
If it doesn’t grow from a tree or in the ground, or swim, or walk don’t eat it.
While “eating clean” and the above categories are actually fairly arbitrary, the “goal” of it all is simple. Don’t obsess about macronutrients. Don’t even obsess about food. Eat a wide variety of plants and animals.

Enjoy your food. Don’t let it take over your life.*

As for the effects of exercise, when you start doing a new type of exercise that your body is unaccustomed to, it breaks homeostatis and forces the body to adapt by developing unused muscles and strengthening connective tissues, which takes energy. This will both build muscle, which increases the basal metabolic rate to sustain muscles, and encourages blood flow and development in that area. If your diets doesn’t increase in intake then you will probably use body fat reserves to power this at least in part, which can result in a transient reduction in body fat and perhaps weight, although the loss of relatively buoyant fat mass may be replaced by more dense muscle mass, and so gains in muscle tone may seem to mask expected loss of body weight. If the exercise does not progressively increase in intensity, the body will eventually return to homeostasis, even if you exersize for longer or with more frequency, hence why weightlifters and gymnasts have to increase their weight or positioning to progress to their goals. Because of this some form of weight/force training, whether bodyweight exercise, plyometrics, or static lifting/pressing is really important to changing body composition and keeping unwanted fat off rather than just relying on cardio.

But again, diet is the most crucial aspect in preventing unwanted fat gain, and that is best controlled by eating a well-balanced diet with generally low GI fruits and vegetables, a variety of plant matter including leafy greens, an appropriate amount of protein and fats, and minimizing highly processed foods.