Why Diets Fail Bodyweight Regulation #lession2

I mentioned in chapter 1 the rather dismal success rates for weight loss (and most types of behavior change). Again, the typically claimed statistic for dieters is that 95% will regain all of the weight that they lost within a few years. The reasons why are the topic this and the next few chapters. Now, one of the longer standing debates, with a lot of flip-flopping over the years is whether diets are failing for biological or psychological reasons. Now, first off let me say that the distinction is a false one and you can’t ever separate the two: biology affects psychology and psychology affects biology.

However, for the purpose of this discussion and this article, I’m going to make that very separation. Just realize that I’m only making it for convenience. At the end of the day, both biological and psychological factors are interacting and solving (or even trying to solve) the problems associated with long-term weight maintenance mean dealing with both. In this chapter, I want to deal with the biology of dieting and bodyweight regulation (this will make more sense in a second), in the next chapter, I’m going to deal with some of the more psychological/behavioral factors that tend to make long-term weight loss an issue. I should note that if you’ve read either of my other, you can probably skip most of this, there’s nothing much new here. If not, please read this chapter first. What is regulation?

To understand what I’m talking about when I refer to bodyweight regulation, I should probably define what it means for a system to be regulated in the first place. When a system is regulated, that means that it attempts (through whatever means) to maintain itself around some predetermined level. The example I’ve used over the years is of the thermostat in your house so that’s what I’m going to use here.

So let’s say that you set the thermostat to some temperature, let’s choose 70 degrees. Now, the thermostat has a thermometer in it which is keeping track of the temperature. If the temperature goes much below 70 degrees, the heat turns on; if it goes much above 70 degrees, the air conditioner comes on. The end result is that the temperature in your house will stay, within some range, around the temperature you have set the thermostat to. That’s a regulated system. You can probably think of other regulated systems, an easy example might be the cruise control in your car. You set it to a certain speed and the car has a measurement device that changes how much gas is going to the engine depending on your speed: when the car slows down, more gas is given so that you speed up; when you start going too fast, less gas is given (or the brake is applied). Of course, in both systems, the change in output (temperature or speed) changes the input, which is how the system stays regulated: it’s just a giant loop. So the temperature drops, the thermostat senses it, the heat comes on, which increases the temperature, which the thermostat senses, turning the heat off. Schematically, the system looks like the following.

What is regulation?

To understand what I’m talking about when I refer to bodyweight regulation, I should probably define what it means for a system to be regulated in the first place. When a system is regulated, that means that it attempts (through whatever means) to maintain itself around some predetermined level. The example I’ve used over the years is of the thermostat in your house so that’s what I’m going to use here.

So let’s say that you set the thermostat to some temperature, let’s choose 70 degrees. Now,the thermostat has a thermometer in it which is keeping track of the temperature. If the temperature goes much below 70 degrees, the heat turns on; if it goes much above 70 degrees, the air conditioner comes on. The end result is that the temperature in your house will stay, within some range, around the temperature you have set the thermostat to. That’s a regulated system.
You can probably think of other regulated systems, an easy example might be the cruise control in your car. You set it to a certain speed and the car has a measurement device that changes how much gas is going to the engine depending on your speed: when the car slows down, more gas is given so that you speed up; when you start going too fast, less gas is given (or the brake is applied).

Of course, in both systems, the change in output (temperature or speed) changes the input,which is how the system stays regulated: it’s just a giant loop. So the temperature drops, the thermostat senses it, the heat comes on, which increases the temperature, which the thermostat senses, turning the heat off. Schematically, the system looks like the following.
Bodyweight regulation

Now, many, if not most systems in the human body are regulated. Consider body temperature where the body strives to maintain a rather normal level (98.6 Fahrenheit in the US, I have no idea what that is in Celsius). If you are put somewhere cold, your body will make you shiver, as well as cutting off blood flow to your extremities (this is why fingers and toes get so cold) to try and keep your body heat up. Go into the heat or exercise and your body sweats and increases blood flow to the extremities to try and get rid of the excess heat so that you don’t overheat.

Another highly regulated system is blood pressure with the body making rapid adjustments to try to maintain blood pressure within fairly narrow limits. The body’s blood glucose levels are similar. So is water balance, if you get a little bit dehydrated, your body will change a bunch of processes so that you retain water; if you drink a lot of water, you’ll pee more to get rid of the excess. On and on it goes and if I sat down and thought about it, probably every other system in your body is equally regulated. So what about bodyweight?

After three decades of research and endless argument in the journals, it’s now well established that human bodyweight is regulated (it might be more accurate to say that bodyfat percentage is regulated). Animal studies decades ago demonstrated that the animals would strive to maintain a relatively stable bodyweight. If you diet them down, they will become less active and slow metabolic rate, rapidly returning to their previous weight when you give them access to food. The same worked in reverse, overfeed them and they will turn off hunger and increase activity rapidly returning to their previous weight.

In humans, studies had demonstrated that metabolism would slow more than you’d predict (for the weight loss) when you dieted people. To a smaller degree, metabolism would also go up when you overfed them. As well, appetite and activity would change accordingly: activity would go down and appetite would go up when people were dieted and activity would tend to increase and appetite would go down when you overfed them. All of which tended to affect bodyweight/bodyfat.

In essence, the body is more or less trying to maintain a given level of bodyfat, that level being called the ‘setpoint’. I should mention here that not all scientists agree with the idea of a rigid setpoint,they prefer to think in terms of a settling point, that is a bodyweight/bodyfat level that you will settle at depending on circumstances of diet and exercise. This would be roughly equivalent to setting your thermostat higher in the winter and lower in the summer or the cruise control faster on the freeway and slower in town (where the speed limit is lower). You pick a different set(tling) point depending on the circumstances.

So a given individual might settle at one bodyfat level (and maintain around that level fairly closely) if they were inactive and eating the modern American diet and settle at a different (and generally lower) bodyfat level if they start exercising and eating better. They would regulate just fine around those settling points (i.e. their bodyweight would fluctuate a little bit) but they’d have to change habits to alter the settling point very much.

If you think about this within the context of human weight gain, the idea of a settling point is probably a little closer to the truth: people don’t continue gaining weight indefinitely. Rather, based on their environment (and, of course genetics), they gain some amount of weight and then stay pretty stable around that new weight. So while you may have weighed a fairly lean 150 in college, when you were active and too poor to afford a lot of food, you stayed around that level of weight. Now that you’re older and less active (and can afford more food), you’re maintaining at 180 or 200, but you’re not continually gaining weight.

Anyhow, the issue of set vs. settling points is sort of tangential to the topic of this chapter. The main idea I want you to take away from this is that within some range, the body appears to ‘defend’ (another way of saying ‘regulate’) bodyweight against change to some degree or another. By ‘defend’, I mean that it adjusts its physiology to try and maintain that set/settling point within a certain range. Towards this goal, the body can, in premise anyhow, adjust metabolic rate, appetite and a whole host of other systems up or down to try and defend against changes in bodyfat or bodyweight.

The physiology of bodyweight regulation: a (very) brief primer So let’s say you go on a diet, increasing activity or decreasing food intake. Your body senses this and should decrease metabolic rate, increase appetite, decrease activity levels and make fat mobilization and loss more difficult in response. This would make it progressively more difficult to lose weight and easier to regain the lost weight once it was lost. Depending on a host of circumstances, including gender, genetics, and starting bodyfat percentage (with some others), the body does this pretty well.

Both during a diet as well as afterwards (in what are called the ‘post-obese’), metabolic rate tends to be depressed, fat mobilization and burning is decreased, appetite and hunger are increased, and there is a host of other stuff going on. This all serves to make regaining fat after the diet that much easier, something anyone who has fallen off their diet knows all too well: the fat comes on much more rapidly then it came off. I should mention there that this is part of the reason that exercise has been shown to have a greater effect at helping to maintain weight loss than to increase weight (or fat) loss on a diet: exercise helps to offset some of the negative adaptations that occur after weight loss.

In the reverse direction, the body should increase metabolic rate, decrease appetite, increase activity and make fat mobilization easier when you gain weight. However, for reasons discussed in detail in website, the system is asymmetrical and most people find it far far easier to gain weight than to lose it. The basic reason, for folks who didn’t read the article, being that getting fat was never a problem during our evolutionary past, while starving to death was a very real possibility. So, unlike animals (for whom getting fat means becoming something else’s lunch), humans never evolved a good defense against gaining weight. In general, we gain weight pretty easily (as the rapid increase in obesity in the modern world demonstrates) and lose it with more difficulty.

I should mention that a lucky few appear to resist weight gain, their bodies tend to radically increase caloric expenditure and decrease appetite when they start to overeat or gain weight.However, they are in the minority. There is also a group of people who seem to lose weight and fat fairly easily, they too are in the minority.Depressingly enough, the same people whose bodies resist weight gain the most tend to lose weight the most easily and vice versa: people who find weight loss the most difficult find weight gain relatively easier.

Researchers refer to these as spendthrift (lose weight easily, gain weight with difficulty) and thrifty (lose weight with difficulty, gain weight easily) metabolisms and are busily trying to determine the mechanisms behind the spendthrift metabolism so they can figure out ways to help the thrifty metabolism people. Until the mechanisms behind the different types of metabolism are determined and solutions (which will either require long-term drug intervention or gene therapy) are developed, dieters simply have to accept that some people will have a harder time than others.

How does this work?
Ok, now I don’t want to get too deeply into the details of this system, to say it’s complicated is an understatement of epic proportion. Rather, I want to discuss the basics since it will be important later in the website. The key factors to remember from the thermostat example is that there is a source of input (the temperature), a measurement device (the thermostat/thermometer), and a source of output (in this case, signals to the heater or air conditioner). And, of course, the output then affects the input, forming a loop.

The equivalent of the thermostat in the temperature example above is a part of the brain called the hypothalamus. This is where the body’s setpoint is both set and monitored. Sort of tangentially, how the setpoint is set is still being researched. Some of it is assuredly genetic, some people are simply born with a higher setpoint than others. Their bodies regulate bodyweight normally, they simply do it at a higher level of weight/fat.

There also appear to be critical periods in development, while you were a fetus, immediately after birth, puberty and pregnancy are a few places where the setpoint can change (almost always going up) based on the environment (mainly nutrition and food intake). There is also some evidence that becoming and staying fat can almost permanently raise the setpoint. There is almost no data indicating that the setpoint can ever be brought back down, at least not within any reasonable time span.

Studies of both animals and humans who have maintained weight loss for several years shows no spontaneous recovery of metabolism, it remains slightly depressed. My best guess: if the setpoint ever comes back down, it does so after years and years and years of maintaining a lower weight. In that most people will regain the weight within a few years, this is the same as saying that it never happens. Anyway, what is the hypothalamus monitoring, what’s the source of input? For years, this was the primary question, what was the signal that told the brain what was going on. In 1994, a hormonecalled leptin was discovered and since then, research has identified a number of hormones within the
body that essentially ‘tell’ the hypothalamus about the current state of your bodyweight/bodyfat level. They also inform the hypothalamus about how much you’re eating.

These hormones include leptin, insulin, ghrelin, peptide YY, glucose and probably several others (don’t worry too much about the names here). The levels of these hormones change when you undereat/lose fat or overeat/gain fat, causing further changes in the levels of various neurochemicals in your brain (the names of which are not important here). Those changes essentially ‘tell’ your hypothalamus when it’s moving away from the setpoint and it takes action.
And what are those actions, that is what’s the output? Well, metabolic rate can be adjusted upwards or downwards due to changes in nervous system output and levels of thyroid hormone.

Appetite and hunger can change, sometimes drastically. Spontaneous activity can go up or down which is part of why people tend to get lethargic when they diet. Levels of other hormones such as testosterone, estrogen and progesterone can be affected. This is part of why dieting tends to affect women’s menstrual cycle and why men who get extremely lean can have problems with libido or sexual function. That’s only a partial catalog of the changes that occur. Those changes further affect bodyweight and food intake which changes the input and that’s how the regulatory loop is formed. This is shown schematically (vastly simplified) in figure 2 below.

Basically, the brain more or less adjusts the function of the entire body in terms of metabolism, appetite, activity, and hormones when you either undereat or overeat. In general, the response to overeating is the opposite of what happens with undereating: metabolism increases, appetite goes down, spontaneous activity increases, hormonal status improves. But, as I mentioned above, the system is not symmetrical and the body is far better at defending against weight loss than weight gain for most people. As well, women tend to better defend against weight loss than men for some rather clear evolutionary reasons (discussed, again, in their bodies fight back harder against diet and exercise programs.

I’m not going to go into much more detail about the system than that, I just wanted readers to have an overview since later chapters dealing with structured refeeds and full diet breaks will make mention of such in terms of how increasing caloric intake can help to fix some of the hormonal problems. In the next chapter, I want to discuss some of the psychological/behavioral reasons why diets fail.