eating to fuel your body (very long)

I've been seeing a lot of posts recently questioning whether to eat your exercise calories. I would like to make an attempt to resolve this question with science and a better understanding of how our metabolism works.

So when members on MFP say to eat your exercise calories, we aren't doing this out of ignorance, or to sabotage anyone's efforts. There's solid science behind it.

Please note, I'm not a Doctor, nor am I a dietitian. I'm just a trainer who's gone through the weight loss ride myself (55 lbs), and have been researching and helping people for a number of years.

First let's clear something up.

If you're obese, or morbidly obese, generally you can get away with not eating all (and in some cases eating none) of your exercise calories. This is simply because the body doesn't care where it's calories come from, sure it will try to use food eaten first, but if there isn't enough,it has no problem taking it's calories from fat and even protein that we have already within our body (body fat and muscle). So the more fat our bodies have, the more surface area of fat we have, and this means we have more available fuel. so if someone's talking about eating your exercise calories, and you know that you have lots and lots of extra fat hanging around (no pun intended) then you can usually safely ignore this statement (by saying something like: "I understand the concept, and will implement it when it becomes necessary, but for now I'll just keep burning extra body fat").

With that said, I'll dig a tiny bit deeper into why we say eat your exercise calories.

So even if you have a decent amount of body fat (say a BF% of around 30 to 40%) that doesn't mean your body can get at all of it right away. At any given moment, your body can only use so much fat as fuel. So when you eat at a calorie deficit, the ideal thing to do is create a deficit that exactly equals the amount of fat your body can mobilize and convert to fuel. Obviously we can't know for sure how much that is as there's no exact formula for this, and without very detailed blood tests, you really can't know. But we can estimate, based on prior research. Essentially through years of study and research, it's been determined that the normal peson (fat not widthstanding) can burn between 0 and 1000 calories a day in stored fat. Very obese people fall outside this spectrum (on the high side) and very small people sit on the low end of the spectrum (either people with low body fat % or people with naturally small frames that have a smaller foot print and therefore less fat to mobilize at any one time).

So what happens when you have a deficit already and then exercise? Well, since you're already at a deficit (and assuming you're being reasonable and not overdoing it) when you add exercise to the picture, you add more calories burned to your total daily energy expendature (TDEE). That means in order to stay within the range that I stated before (0 - 1000), you would have to add calories to your diet. You would still stay within your deficit range if you did so. As you can see, eating exercise calories doesn't diminish how much you would lose, it just keeps the metabolism stable. We talk about eating exercise calories not to make it take longer for you, but to allow you to lose weight in such a way that you can continue for life, this is a lifestyle change, not a quick fix.

things that can derail this process.

1) You're trying to lose too much too fast. 2 lbs a week isn't for everyone, most people who are in the overweight category should never attempt more than 1 lb per week. You simply don't have the body fat stores in order to make up the difference. You'll end up making it harder.

2) You've been eating so low for so long that your body has adjusted to it. In this case, if you immediately start eating your exercise calories, you're bound to gain weight for a month or more before your body corrects itself, and allows you to again begin burning fat stores. It's better to raise your calories by about 50 or 100 a day, every week (I.E. week one add 50 to your daily calories, week 2 add another 50 ...etc.) Until you reach something close to maintenance, give it 3 or 4 weeks, then begin your deficit. I know this sounds long and torturous, but it's the ONLY way to do this right, and you'll probably notice how easy it becomes when you do this. And in the long run, is one month really that much?

3) Underestimating your food, overestimating your exercise calories, or more likely, both. I'm shocked at how few people know what a serving of food is. It's more common that people realize to make incorrect guesses about their consumption. I usually tell people to measure their food, and don't go out to eat for at least 2 to 4 weeks on a new nutrition plan, until they become more confident in what a meal SHOULD look like.

4) starvation mode. this ties in with number 2 closesly. Starvation mode is real. Eat far under your maintenance for too long and your body WILL fight back, stripping you of infrequently used muscle, slowing down organ productivity, and in some cases completely shutting down organs. This is real, it does happen and it can inhibit weight loss. PLEASE note, I didnt' say it will make you gain, it won't although if you read 2 you can see how you can gain weight while in starvation mode (but only when you up your calories drastically and quickly)

5) Eating only when you are hungry. This is a bad move for people who have abused food in the past (either by under or over eating). Your hunger response is based on hormones. When you eat too little or too much for a long period, the body can either stop sending the hormones (correctly) or send them when they aren't needed. If you aren't at a good body fat % and aren't sure your eating healthy, then don't trust hunger. It's safer to rely on a plan that you are confident in, stick to it, and allow your body to fix itself.


Obviously with regards to all of this, it refers ONLY to people who are (besides their weight) otherwise healthy. If you have metabolic conditions (I.E. diabetes, thyroid issues, metabolic syndrome...etc.) then this doesn't necessarilly hold water and you should go on the experienced advice of meical experts. And truly, I KNOW some of you have done it other ways, really I do, it's a testament to the human machine that we can do this, none-the-less it's anecdotal and really can't be used as an example of what to do, there are just to many variables to take one or two or even fifty examples and call it truth.

Hope this clears some things up

-Banks