Ok, well, as always, in looking for good information on fitness and nutrition, one of my first stops is
Dr. Hussman's website. I'm pasting below a bit of information from his discussion of nutrition.
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Your raging metabolism
Let's talk about your metabolism. Yeah, I know it's too slow. No doubt, you've got the fat gene too. Probably from both sides. I'm kidding, of course, but it's amazing how many people talk quite authoritatively about their metabolism being slow without actually knowing what metabolism is, or what they can do about it.
There are three components to your metabolic rate:
Base Metabolic Rate or BMR. This is the amount of energy your body would use simply by lying around in bed all day. You increase your BMR by building more muscle, which is metabolically active. You'll find a calculator to estimate your BMR in the "How calories work" section below.
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Unrestricted Physical Activity or UPA. This is the amount of energy your body uses during daily activity. You increase UPA through exercise, and also by doing physical activity throughout the day (take a walk, take the stairs, choose a more distant parking spot).
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Thermal Effect of Food or TEF. This is basically the second law of thermodynamics at work - converting energy from one form to another is never 100% efficient. So eating typically throws off a modest amount of energy as heat. You increase TEF by eating small, frequent rations containing mostly protein and carbohydrate. Unfortunately, since the body stores excess dietary fat directly as body fat, there is no need to convert it, so eating fat generates virtually no thermic effect at all. Now, don't kid yourself that eating more food is a way of burning calories. But for a given "budget" of calories you eat in a given day, it's better to spread those calories out across several small rations containing protein and carbohydrate, rather than blowing the budget on a couple of larger or higher fat meals.
Metabolism includes two groups of chemical reactions in the body:
Anabolism - which is creation or "building up", and
Catabolism - which is destruction or "breaking down"
There are a lot of people who simplistically believe that you can't build muscle and burn fat at the same time, since building muscle is anabolic and burning fat is catabolic. This is wrong, but it's wrong in an interesting way. Clearly, you can't be anabolic and catabolic at full-throttle in the same instant, but you can certainly affect your body's ability to accomplish both during the day.
There are dozens of chemicals and hormones involved in regulating metabolism, but for practical purposes, two that you have the ability to do much about. They are insulin and cortisol.
Insulin is one of the main anabolic hormones in the body. The only way that glucose (sugar) can get into the cells to be used as energy is for it to be accompanied by a little insulin guy. Insulin does two things: it says "Hey, we've got sugar in the bloodstream here. Stop burning fat so that we can get rid of this stuff first." And then the insulin helps to transport the sugar into the cells.
So insulin is "anabolic". It helps the muscle cells to get fed. Well, muscle cells and fat cells. If your muscle glycogen stores are full, insulin feeds your fat cells instead. If you spike your insulin higher by eating a significant amount of simple carbohydrates (such as sugar) when your energy stores are full, the excess carbs are converted to fat and escorted to your hips. The insulin then causes a subsequent plunge in blood glucose, often followed by fatigue. Brain cells can't store glucose, so that plunge in blood glucose can also cause dizziness. So, too much sugar and you may find yourself saying "I'm fat because I'm tired, and I'm tired because I'm fat." Bottom line: insulin is triggered by the consumption of simple carbohydrates. Except when you want to intentionally spike your insulin levels, you should choose carbohydrates that trigger a minimal release of insulin. These are called low-glycemic carbohydrates.
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If you're serious about taking control of your nutrition and managing your health overall, I strongly urge you to visit Dr. Hussman's site. He's amazing, and there's a wealth of credible, respected information to be found there.