A strange topic for me to be writing about, eh? I've recently been trying to lose weight, having gained a considerable amount over the last 6 or 7 years, and so it's had me thinking about the dynamics of weight loss and why certain diets seem to work, but others don't.
I've always been a big carbohydrate eater. Breads, sugary foods and drinks, cereals, pastas - these have always been the most significant parts of my diet. I also have tended over the years to overeat on a magnificent scale. I'm one of those people that can put others in awe of my eating prowess.
So in order to lose weight, I decided to go on a low-carb diet for a few weeks to get the ball rolling on weight loss, then readjust later to a normal diet with a reduced overall caloric intake. I haven't yet gotten to phase 2 - that will begin in a week. I don't own a scale, so I can't say how much weight I've lost, but I can tell I have trimmed down.
In any case, I thought it might be helpful to share some of the things I am learning about the dynamics of weight loss.
To begin with, it might be instructive to provide some basics about human energy and nutrition. When people talk about losing weight, the first thing they always mention is that dreaded word "calories." It seems as though a lot of folks imagine calories to be these little particles in food that enter your body and determine whether you lose weight or gain weight.
A calorie is simply a unit of energy, in the same way that a centimeter is a unit of distance. Quite literally, a nutritional calorie (also called a kilocalorie) is the amount of energy required to heat one liter of water by one degree Celsius. Therefore, if you have one liter of water, with a temperature of 45 degrees Celsius, how much heat energy would be required to make it 46 degrees? Answer: one calorie.
So a nutritional calorie is simply a unit of measurement that tells us how much energy we are consuming.
The human body, of course, requires energy to stay alive. Your muscles, bones, and organs all require energy in order to function. We get that energy from the foods we eat, because our bodies convert those foods into calories - units of energy to fuel our bodies. A car won't run without gasoline; it burns gasoline as energy. Similarly, our bodies won't run without food because our bodies burn food as energy. And we measure that energy in calories.
The human body is able to convert three types of food into energy - carbohydrates, fats, and proteins. The number of calories (i.e., the amount of energy) the body can get from these sources depends on the amount of food eaten and the type of food. Generally-speaking, one gram of fat will provide nine calories, while one gram of carbs or protein will equal about four calories. Anything else you eat provides 0 calories - that is, no nutritional or metabolic benefit. It just passes right on through.
Most people understand what fat and protein are - fat is, well, fat, and protein is the stuff that builds muscle tissue and plays a role in numerous chemical processes in the body. Carbohydrates are a little more confusing, because there are so many different kinds. As a general rule, carbohydrates can essentially be thought of as sugars. That doesn't mean, of course, that foods high in carbs will necessarily be sweet (see bread, pasta, and potatoes), but when you ingest carbs, they end up functioning like sugar in your body.
We've seen that the human body turns nutrients in food (carbs, fats, and proteins) into energy (calories) in order to keep itself alive and healthy. So how many calories does your body actually use on a day-to-day basis? This number is referred to as the "base metabolic rate," and it refers to how many calories your body uses each day simply keeping itself alive. Imagine that you lay in bed from midnight to 11:59 p.m. - 24 hours - and do nothing but sleep or read or watch TV. How many calories would your body burn in that 24-hour time period? The answer is your base metabolic rate, and that will vary depending on your age, height, and weight, as well as several other factors. There are common formulas you can use to figure out your own personal rate; mine is about 2300 calories per day. So if I did nothing at all but lay in bed or sit on the couch for 24 hours, I would burn about 2300 calories. That's how much energy my body would require to keep my heart beating, my lungs working, my neurons firing, etc. Now, I am 6-foot, 3-inches tall, and weigh about 250 pounds. Someone much smaller than me will, of course, have a much lower base metabolic rate. I have a big body, so it takes a lot more energy to keep me going.
If I get up off the couch and engage myself in some kind of physical activity (washing the dishes, going up the stairs, blogging, running a mile, climbing a mountain), then I will burn even more calories, depending on how much activity I am actually engaging in. This is why exercising is regarded as a way to "burn calories." You use up more energy (more calories) if you actually get up and do something. I've been able to determine that because of the physically-active nature of my job, I may burn as many as 3500-4000 calories per day (which would be the sum of my base metabolic rate plus my daily activities). I should have no problem at all losing weight, but this just goes to show you how much I tend to overeat.
The human body's preferred source of energy is carbohydrates. (Some low-carb diet gurus dispute this, suggesting that because the earliest humans were hunter-gatherers, and thus had meat-based diets, the most "natural" form of human metabolism comes from fats and proteins. Most nutritionists, however, don't buy that argument, but to explain why would involve a very long and boring discussion of human biochemistry and physiology, and I don't want to get into that here. Suffice it to say, the prevailing belief is that carbohydrates are the body's preferred source of energy).
As a result of this, the human body will always burn carbohydrates for energy before touching fat or protein. Therefore, if you eat a diet high in carbohydrates, your body will tend to simply use those carbs for energy, and whatever fat you eat will, quite literally, go to your gut. I can testify personally to this phenomenon. This is one of the reasons why low-carb diets work so well for quick weight-loss. If you cut out your body's preferred source of energy - carbs - you effectively force it to burn fat instead. And since you probably won't consume enough fat on any given day for your body to meet its nutritional needs, you will end up burning fat stores (adipose tissue) from your body to get energy. Thus, you trim down quickly, even without adding any new exercise routines.
This is also the reason why low-fat diets so frequently fail for people. When you eat a low-fat diet, you are, by necessity, eating a lot of carbs (low fat foods tend to be high in carbohydrates, and vice versa). Thus, your body burns those carbs for energy, and even though you aren't adding much new fat, your body never gets through all the carbs in order to get to the fat. So you may diet for weeks and never lose much weight. You have to dramatically increase your activity level in order to burn enough calories on any given day to burn through all the carbs and get down to the fat. This is why exercise routines almost always accompany low-fat diets. This is also why low-carb diets are so alluring. You don't have to change your level of physical activity: you just burn fat - and lose weight - because you've taken away the carbohydrate source.
While most nutritionists agree that low-carb diets can help a person lose weight quickly, they also warn against eating a low-carb diet for a long period of time. There are several reasons for this. First, the kinds of foods you eat on a low-carb diet tend to be foods that are not so good for your heart, brain, and other organs. Secondly, when you force your body to burn fat instead of carbs, it releases fatty acids into your blood stream, and if this happens to a great enough degree, it can actually cause a very serious medical condition known as ketoacidosis. This is where the pH balance of your blood gets off-kilter because of high acidity. Now, it is unlikely that this condition would occur in a healthy person with a normally-functioning liver and pancreas, but it's not outside the realm of possibility, depending on just how "low-carb" you take your diet. That's why many low-carb diet gurus suggest a carbohydrate intake of 60 grams or so per day (as opposed to the famous Atkins diet, which, in its first phase, limits the dieter to a mere 20 grams per day).
I read about a study recently that took a group of dieters who were all roughly the same age, height, and weight, and who all had similar levels of daily physical activity, put them into three groups, and gave them different diets to try. All groups were limited to 1500 calories per day. The first group was put on a 1500 calorie low-carb diet. The second, a 1500 calorie low-fat diet. And the third was put on a 1500 calorie low-glycemic diet (this is a diet that primarily limits sugary food - a typical diabetic diet).
After thirty days, they found that the low-carb dieters lost weight more quickly. How could that be? All had similar metabolic rates and daily levels of activity. All were the same weight at the beginning of the study. And all were limited to 1500 calories. One would assume that they would all have lost about the same amount of weight. And yet the low-carb group lost significantly more. It would appear, for whatever reason, that the human body simply burns carbohydrate calories more efficiently.
Let me explain that. The group eating a low-fat/high-carb diet lost weight more slowly than the group eating a low-carb/high-fat diet. This must imply that when the human body is getting the majority of its calories from carbs (a low-fat diet) it does not require as many calories to do the same amount of work. In other words, the human body doesn't use fat calories nearly as efficiently, and thus requires MORE calories to do the same amount of work, if those calories are coming primarily from fat. It's sort of how Gasoline A might give your car 25 miles per gallon, but with Gasoline B, you get 30 miles to the gallon. Your car burns Gasoline B more efficiently. If you use Gasoline A, you need MORE gas to go the same distance. Similarly, if you are burning mostly fat for calories (a low-carb diet), your body has to burn MORE of it to do the same amount of work.
Now, that's my own take on the study. The people who performed the study actually said they weren't sure why the low-carb dieters lost more weight. But it seems to me that perhaps a carb calorie is not equal to a fat calorie in practice, even though in theory it should be.
I have read some criticisms of low-carb diets that suggest that the real reason people lose weight is not because of the lower carbs, but because of a phenomenon known as "spontaneous reduction in food intake." Put simply, when you go on a low-carb diet, you are more likely to dramatically lower your total caloric intake than when you go on a low-fat diet. The reason why is simply because low-carb diets are far more restrictive on the types of foods you can eat than low-fat diets are. On a low-fat diet, you can still eat a significant number of overall calories, and you are more likely to do so simply because you have removed high-fat foods that tend to be filling. On a low-carb diet, however, you cut out a significant number of foods that dramatically limit what you can actually eat. Furthermore, you tend to eat high-fat, high-protein foods that are very filling. So in the end, you end up spontaneously eating far fewer calories, even though you aren't actually counting calories as part of your diet. I can also personally attest to this. While I have been eating low-carb, I haven't been counting calories. But I know, based on my own past eating habits, that I am eating far fewer total daily calories, because the meat-based diet I am eating fills me up quicker, and I also skip all those high-carb snacks that I used to eat between meals.
Of course, there's still that study I read about recently that DID count calories, and yet still found that low-carb dieters lost weight faster than low-fat dieters.
In any case, I am convinced that a low-carb diet is a fantastic way to shed pounds quickly, if you are significantly overweight (I am just inside the "obese" category on the Body Mass Index scale). It's also good if, like me, you have a tendency to binge on carbs. But once you've lost that initial weight and have reached the point of maintaining a healthy weight, I am equally convinced that carefully watching your total caloric intake is the best way to go. The body needs carbs, it needs fat, and it needs protein. It works best, I believe, when it has a healthy combination of all three. If you know what your base metabolic rate is (and it's easy to find out), then you can figure out very easily how much food you need to be eating on a day-to-day basis to maintain your weight. In the long-term, the healthiest choice is simply to cut back on how much food you eat and stay active, but keep your diet varied and allow yourself to eat the foods you like, so that you can avoid feeling deprived. Deprivation of your favorite foods is a sure road to binge-eating and weight gain.