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Bulletin #74 – Controlling Body Fat Metabolism, Part I

One topic virtually everyone (with the possible exception of Sumo wrestlers) is concerned about is fat metabolism. Depending on how we define ‘fat’, about one-half of all Americans are considered overweight. One-third can be categorized as obese. These numbers are shocking and underscore the fact that most Ameri-cans just don’t eat properly or exercise enough. A century ago the big problem in nutrition was nutritional deficiency. Now our problem is excess body weight. It has been said that America is the only country where even the poor people are fat. Over the eons people spent much of their day, and a lot of energy, gathering and prepar-ing food. Now you can order a pizza over the phone and have it delivered to your door. Food is readily available here, and it’s cheap, convenient and fast. You get a hamburger and fries without getting out of your car and there are vending machines at work loaded with candy bars and chips. Is it any wonder that Americans are fat?

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Many people want to eat right and try to lose weight, but they don’t know what to do. There are low-fat diets, high-fat diets, low-carb diets, rotation diets, fruit diets and every other type of diet imaginable. To make matters more confusing, they all work and they all don’t work. I’ll explain this seeming contradiction later . There is a lot of confusion about the best way to go and this is understandable given that even scientists and doctors cannot agree . Be-fore I get into the biochemistry and physi-ology and show how that helps us decide on the optimal diet, let’s just talk about some very simple general principles with which I think most people will agree. My first general concept is that to lose fat and keep it off requires a permanent lifestyle change. Many people use a calo-rie-restricted diet for a period of time, reach their goal weight, then go off their diet and resume their previous way of eating, change that produces temporary results. If you want permanent results you need to make a permanent change. You need to pick a diet program with which you can live.

An all fruit diet or a zero carb diet might make you lose weight, but is clearly a bad choice because you can’t live that way forever. My second general concept is simple: to achieve a lean, healthy, beautiful physique requires exercise as well as a proper diet. This is a big problem for many Americans who don’t have time, energy or motiva-tion to exercise. Let’s face it, Americans are lazy. We work hard and long hours but for most of us it is not work of a hard, physical nature. After work we are tired and don’t feel like exercising. We work hard in the stressful sense, but as a society we are physically lazy. That’s a big reason why, as a nation, we are fat. Most of the hard physical work these days is done by machinery. If you exercise enough, that can make up for a lot of dietary indiscre-tions. Marathon runners, for example, can eat as much as they want and still be skinny. On the other hand, if you don’t exercise your metabolism is so slow that even a small amount of food can make you fat. We deal with a lot of clients (mostly women) who try to starve themselves thin, yet they cannot lose weight no mat-ter how little they eat.

I will say, almost without exception, that these people are eating too little and not exercising enough. Exercise increases your muscle mass, which in turn increases your metabolic rate and helps you burn fat. Eating more and exercising helps people build muscle. Muscle is the engine that burns fat. When we encounter someone who has been on a low calorie diet for a long time and just can’t lose weight (and we see this situa-tion practically everyday) we will have them increase calories and exercise. We actually ask them to gain a pound a week for the first four weeks following our diet parameters. Chronic caloric deprivation lowers the metabolic rate as your body adapts to the reduced energy intake by re-ducing energy expenditure. After just one month on this program, these individuals find the fat melts off. Dieting alone won’t work optimally, even if it is a proper diet. If you lose weight by caloric restriction alone, with-out exercise, up to half of the weight you lose will be muscle.

This approach will also slow your metabolic rate, prevent-ing further fat loss even on a low calorie diet. Exercise builds muscle and protects against the loss of lean mass while you shed fat. This approach maintains a high rate of metabolism, allowing continued fat loss. What about the person who re-fuses to exercise? You can get leaner and healthier through diet alone, but you’ll go much further and get there much faster of you include exercise in your lifestyle. My third general concept gets back to this idea that all diets work, and all diets don’t work. Allow me to explain: any en-ergy (calorie) deficient diet will result in weight loss. All diets, no matter how crazy or unsound, will work to produce weight loss if they don’t supply enough calories to meet the body’s needs. This physiolog-ical fact-of-life contributes to the state of mass confusion. (Bad pun, sorry!) Diets fail because they produce results only as long as you remain on the diet . Once you go off the diet and eat ‘normally’, you gain the weight back. One leading obesity researcher put it like this: all diets work, it is the maintenance programs that fail. In other words, most people can starve themselves temporarily and lose weight, but are unable to maintain their reduced weight.

There are two reasons for this. The whole concept of going on a severely restricted diet to lose weight is physi-ologically unsound and simply activates the body’s defense mechanisms against weight loss. Secondly, most people have no idea what a maintenance program is, or what to do. How about this as a con-cept: what if we just go on a maintenance plan at the beginning and just skip the low calorie diet? A maintenance diet is the long-term diet that we intend to use for the rest of our lives to maintain our reduced bodyfat state. If this diet works to maintain the reduced state, it will work to produce that state. The reasons for this have to do with the thermodynamics of steady state energy and nutrient balance: which I have discussed in detail before. I devoted two or three articles to this topic about a year ago and it’s too much to repeat it all here . Check out our web site at for past articles in the Sports Nutri-tion Guide.

Suffice it to say temporary low calorie diets backfire because they slow down your metabolic rate. You’re better off picking a program from the outset that you can tolerate for the rest of your life. You need to get enough to eat and not feel deprived. That is what the Parrillo Nutrition Program is all about. With that as an introduction, we can now proceed to discuss some details of how fat metabolism is controlled. Once we understand my three general concepts, how to design a proper diet will be made clear. As usual, we will start with the ba-sics and work into the details as we go. After a meal the body has abundant car-bohydrates (we’ll discuss low carb diets later) and this stimulates insulin release. Insulin in turn stimulates cells to absorb the glucose and use it for energy. Insulin exerts its greatest effects on muscle, fat, and the liver. Glucose is absorbed and used as fuel and the excess is stored as glycogen. (I’m glossing over this because we discussed it in detail in the last two months’ articles about insulin.) After the meal has been digested and absorbed and glucose has been taken-up by cells, eventually the blood sugar level starts to drop. This will result in decreased insu-lin levels and increased glucagon.

This hormonal shift causes the liver to slowly break down the glycogen it stored from the last meal and release the glucose into the bloodstream. One of the main jobs of the liver is to maintain a relatively uni-form blood-glucose level between meals. This provides a steady supply of blood sugar for the brain. Another important property of insulin is that it blocks fat breakdown and the release of fat from fat cells. Now with insulin levels decreased, the brakes are taken off of fat metabolism. An hour or two after a meal when blood glucose and insulin levels decrease, the body begins to use fat as well as glucose as a fuel source. In this state (called the post-absorptive state), after the nutrients from the last meal have been digested and absorbed, the body relies significantly on fat as a fuel source. This helps save the glucose for the brain, which cannot use fatty acids. Muscles love to use fat as fuel and will do so readily whenever insulin levels are low. The absence of insulin allows fatty acids to be released from fat cells but this doesn’t happen automatically.

Fat break-down has to be stimulated by something. The most powerful stimulus for this is norepinephrine, a cousin to adrenaline . Norepinephrine (NE) is released from nerve endings of the sympathetic nervous system, which impinge upon the fat cells. This molecule acts as a neurotransmitter and provides the direct stimulus for fat cells to release fatty acids into the blood-stream. The fatty acids are delivered to the muscle cells where they are absorbed and used as fuel. What can we do to accel-erate this process? A couple of things are obvious: One is to control insulin levels. At first you might think the best way to do that would be to eat a low carbohydrate diet. Although there are times when that is not a bad idea, usually it is not the best way to go. I’ll get back to that in a min-ute. The second major thing we can do is control overall caloric intake and this is much more important than insulin by itself. Things like diet composition and insulin levels are important and they seem to exert most of their effect at determining steady state body composition. Overall body weight is determined pri-marily by energy balance.

If you eat ex-cess calories, you will not be able to lose fat regardless of how well you control insulin. So you have to eat the appropriate number of calories. We’ll talk more about that too. Third, we have to exercise. Ex-ercise is the most powerful stimulus for NE release at the fat cells—at least the most potent stimulus over which we have voluntary control. We need to exercise to stimulate fat breakdown and the release of fat from adipose depots. Exercise in-creases our rate of energy expenditure and the utilization of fat as fuel by muscles. We are primarily talking about aerobic (cardiovascular) exercise here. The best thing you can do to increase fat loss is to eat the proper number of calories—dis-tributed among the appropriate foods and to exercise. Generally speaking, the more intense the exercise is the more effective it is. This applies to aerobics as well as weight training. How many calories should we eat and how do we construct the proper diet? A pound of bodyfat contains 3,500 calo-ries. This means you must achieve a net energy deficit of 3,500 calories to lose one pound of fat. A good goal, one that I generally recommend, is to lose one pound of fat per week.

This would be an energy deficit of 3,500 calories per week, which equals 500 calories per day. Rather than reduce your caloric intake by 500 per day, a much more effective approach is to reduce your caloric intake by 250 per day (compared to what you normally eat) and then do 250 calories worth of additional aerobic exercise, over and above what you would normally do. Together, these actions will generate a net energy deficit of 500 calories per day, promoting loss of one pound of fat per week. Now you might say, well, I’m too lazy to go to the gym, so how about if I just decrease my caloric intake by 500 per day and don’t do any exercise? This will obvi-ously produce the desired energy deficit, but the results will be terrible using this approach. (Although it is the most com-mon approach to weight loss.) There are many complicated reasons for this, too much to go into the details here. Briefly, the first problem is that up to half the weight lost by simple energy restriction (without exercise) is muscle. So although you lose weight, body composition doesn’t change much, and neither does appearance. You just look like a smaller version of the same shape. We want to change our shape and appearance, not our weight per se. The second problem has to do with complex changes in hormones and enzymes and metabolism. Energy restriction will decrease your metabolic rate as your body adapts to decreased energy availability. To avoid this, do not restrict calories too severely (250 per day less than usual is enough) and exercise. Exercise offsets the decrease in metabolic rate that accompanies dieting . I discussed diet composition last month. To review briefly, carbohydrates are a better choice than conventional dietary fat even though they are a more potent stimulus for insulin release.

This has to do with the thermic effect of feeding (TEF) and the fact that carbohydrates tend to be stored in the body as glycogen, whereas dietary fat is stored as bodyfat. (Go back to the series on nutrient balance for a re-view.) We can still supply the bulk of our dietary energy as carbohydrate without overdoing the insulin response by using some common sense. The most obvious thing is to avoid simple sugars. Supply your carbs as complex carbohydrates. Second, combine starches with fibrous vegetables and protein. These decrease the rate of glucose entry into the blood-stream and greatly moderate the insulin response . Each meal should contain a protein source, a starch and a fibrous vegetable. If you want to reduce the car-bohydrate content of the diet, reduce the starch, especially late in the day. If you need to keep the calories up, use CapTri® or increase the protein but stay away from conventional fat. Next month we’ll get into some of the biochemical details of why this works.


1. For more information about the physi-ology of fat metabolism, refer to Guyton AC and Hall JE. Textbook of Medical Physiology. W.B. Saunders Company, Philadelphia, 1996.

2. For details about the biochemistry of fat metabolism, consult Devlin TM. Text-book of Biochemistry with Clinical Cor-relations. Wiley-Liss, New York, 1992.2. For detailed information about how to construct your diet for optimal body com-position, refer to the Parrillo Performance Nutrition Manual.

2018-03-13T11:10:31-04:00 June 17th, 2009|Technical Supplement Bulletins|

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