Weight gain is not caused simply by taking in more calories than you burn (the so-called “calorie-in / calorie-out” model). Calories in and calories out are interdependent factors, so when calories are restricted the body actually slows its metabolism, lowering the energy it uses for vital bodily functions. Basal Energy Expenditure (BEE) can decrease by as much as 30-50% in order to spare calories!
On the opposite end, when too many calories are taken in by someone who is already overweight, the body will try to get rid of them by increasing its Basal Energy Expenditure, usually by speeding up respiration, increasing heart rate and breathing and generating more heat.
The body does this because its ‘set point’; the weight at which your body likes to be and will tend to stay with very little effort, is highly regulated. It really isn’t that easy to gain or lose weight if we haven’t already compromised this built-in homeostatic mechanism.
That is why trying to control calories doesn’t work for long term weight loss. When we restrict calories, and increase our exercise, our body responds by increasing hunger, initiating craving (especially for foods such as simple carbs that can be broken down quickly to glucose for your blood) and by decreasing the amount of energy it uses.
Have you ever skipped a meal or lowered your calories so much that you feel cold; even though the room is at an adequate temperature and you are dressed appropriately? You are shivering because your body is sparing calories it would normally use for heat generation.
Body Weight is Regulated by Hormones
Body weight is not really under our control as much as we’d like to believe. It is a tightly regulated process that involves a variety hormones including leptin (a hormone that regulates fat stores by inhibiting hunger), ghrelin (a hormone that increase hunger when your stomach is empty) and insulin, which plays a very significant role in hunger, eating behavior and fat management.
To understand how significant a role insulin plays in weight regulation, let’s look at a situation where there is insufficient insulin. Type I diabetes results from the destruction of the insulin-producing pancreatic islet cells stemming from an autoimmune disorder. One of the hallmarks of this disease and it’s very low levels of insulin is severe weight loss. Type I diabetics need to take insulin injections to correct for the insulin deficiency but the more insulin that is taken, the more weight gain there is. As insulin levels go up, hunger is triggered and we feel the urge to eat.
Insulin is one of the major controllers of the body set point.
As mentioned, if we don’t take in sufficient calories, then our body decreases our Basal Energy Expenditure so that we end up maintaining our body weight in response to whatever the number of calories are that we take in. The issue in weight gain is not how to reduce calories but how to reduce insulin.
Insulin as the Main Factor in Weight Gain
When we eat food, our body releases insulin in response to the rise in glucose in our blood, coming from the digested food. Insulin acts as a messenger to instruct the body’s cells to absorb glucose, in effect reducing blood glucose levels.
Insulin resistance is a condition in which the cells of the body become resistant to insulin and fail to respond normally to normal levels insulin, leading to higher blood sugar. The pancreas tries to compensate to this condition by producing more and more insulin. As long as the pancreas is able to produce enough insulin to overcome this resistance, blood glucose levels remain normal but when the pancreas can no longer produce enough insulin, the blood glucose levels begin to rise.
Initially, this added rise in blood glucose happens after meals (when glucose levels are already at their highest) and more insulin is needed – but eventually these higher levels of glucose are seen first thing in the morning when the person hasn’t eaten for 8 or 10 hours. When blood sugar rises abnormally above specific clinical levels, the person is diagnosed as having Type 2 diabetes. Insulin resistance is often called “pre-diabetes” because it precedes the development of Type 2 Diabetes.
Consistently high blood glucose levels along with insulin resistance lead to cells that are starved of glucose even though there is plenty of glucose in the blood. Since the cells aren’t getting any of the glucose even though it is there, it is not available to the cells because insulin is not binding it and taking it in. As a result, hunger signals are sent to the brain, leading to eating, even though the person has recently eaten.
As more and more glucose accumulates (both from the food being eaten and as you will see in a minute, through the making of glucose due to the effect of cortisol, another hormone) the high levels of glucose trigger the body to store the excess glucose as body fat.
The Effect of Stress on Weight Gain
Cortisol, the so-called stress hormone also plays a role in weight gain. Let’s look at another medical conditions to illustrate the effects of cortisol. In Cushing Syndrome, cortisol is over-produced by the body and weight gain results. When we give people a synthetic form of cortisol as a medication (e.g. prednisone) they get something called Cushinoid Syndrome. That is, they look like they have Cushing ’s disease. Not only do they gain weight, but there is a particular distribution of this weight gain called truncal obesity which means that fat is gained around the belly, rather than on the arms and legs.
In adrenal insufficiency (also known as Addison’s disease) which produces the opposite effect, the adrenal gland becomes damaged due an autoimmune condition and is unable to produce cortisol. The hallmark of Addison’s disease is weight loss.
So what role does cortisol play in healthy individuals? Cortisol is released as a result of ordinary events such as waking up in the morning or exercising, but also is released in response to physiological and psychological stress. Physiological stress might be an illness or injury and the release of cortisol services a needed function to make sure we have enough glucose to heal.
Under stressful conditions, cortisol also plays the role of providing the body with glucose by tapping into protein stores via gluconeogenesis in the liver. This energy can be helpful in a “fight or flight” type of stressor, such as when one is being chased by something however under constant levels of psychological stress, elevated cortisol over leads to higher levels of glucose being made from protein in the body the long term. So in addition to glucose coming from the food we eat (exogenous sources), we now have the body making its own glucose (endogenous sources). The combined exogenous glucose from good and the endogenous glucose triggered by cortisol, now leads to even higher blood sugar levels that without the long term stress.
With continually high levels of cortisol, the body will take fat that is stored as triglycerides in our liver and relocate them to visceral fat cells — those under the muscle, deep in the abdomen. Just like in Cushing’s syndrome, we now see truncal obesity triggered by stress, mediated by cortisol.
Weight Gain is due to Hormonal Triggers and not a Lack of Will-Power
Cortisol also directly influences appetite and cravings by binding to hypothalamus receptors in the brain, triggering us to eat and crave foods that are easily broken down to glucose. Cortisol also indirectly influences appetite by modulating other hormones that stimulate appetite. Simple carbohydrates like bread, pasta, candy and pop are common foods that people reach for in response to these craving because they are easily broken down to simple sugars. So, it is actually the higher levels of cortisol that lead to increased appetite and in particular cravings for high-calorie foods, not simply a lack of will-power.
As you can see, we don’t really control our body weight any more than we control our heart rates. To a large degree, body weight is regulated automatically under the influence of hormones; hormones that indicate to eat and indicate when we are satiated. Hormones signal our bodies to increase energy expenditure and when calories are restricted, hormones will slow energy expenditure.
Why All Diets Work and often All Diets Fail
It doesn’t really matter which diet people follow, whether it is Atkins, South Beach, or the good old fashioned low fat, low calorie diet, all diets in the short term produce weight loss. Yes, some are healthier than others, but they all “work”.
One would hope that by continuing to eat according to what ever diet we’ve chosen and by exercising, that our body’s set point would reset at a lower level, but this doesn’t happen.
Insulin levels stay high, continuing to drive hunger and eating.
How does this affect weight loss?
A few months into our diet, regardless what diet we follow, weight loss begins to plateau. As the plateau continues, people get discouraged, and think to themselves ‘if I’m not losing weight, then I may as well eat – fill in the blank’. This is either followed by an abandoning of the diet completely and a regaining of the weight previously lost (or more) or by a stubborn insistence to restrict calories and fat even further — leading to a downshifting of basal energy expenditure. It’s a vicious cycle.
But why does Body Weight Plateau in the First Place?
In response to weight loss, the body tries to return to its original set point. First it slows metabolism to try and slow down weight loss – resulting in slowed weight loss and eventual plateauing.
The reason is because we’ve done nothing to lower insulin levels.
Think of set point like a ‘body weight thermostat’. With a thermostat, when the air is hot enough, the furnace turns off and when it is too cool, the thermostat turns the furnace on. Regardless what kind of diet a person follows, there will be weight loss effects in the short term, but eventually, even with continued compliance, body weight plateaus and in time, the person begins to regain the weight.
What about exercise?
Surely exercise will help us lose weight, right?
Basal energy expenditure which is the amount of energy we use at rest is estimated to be approximately 12-15 calories per pound. For someone confined to complete bed-rest, caloric needs are calculated as 1.2 times Basal energy expenditure (BEE).
To visualize the effect exercise has on calorie loss, let’s take a 140 pound person as an example, whose basal caloric needs are 2200 – 2500 calories per day. Say they start exercising. They start walking at a moderate pace (2 miles/hour) for 45 minutes every day, and burn roughly 104 calories. Let’s look at that in terms of basal energy expenditure – that is only 4% of the BEE. Okay, so say the person starts working out at a more vigorous pace, calorie burning will go up, right? But how much? 6% of BEE? 8% of BEE? That’s about it.
The bottom line is, the vast majority of calories you take it; about 95% of caloric intake is used to heat the body and other metabolic processes, including keeping your heart beating, breathing, digestion, brain function, liver and kidney function, etc.
Set point is a tightly regulated mechanism, like a thermostat. When we burn more calories through exercise two things happen. Studies show that people actually end up decreasing their activity outside of the period of exercise and the other is they increase their caloric intake in response to exercise. That’s where the phrase “working up an appetite” comes from.
The reason exercise is not that effective for weight loss is because of metabolic compensation. We understand this intuitively though, don’t we? When know when we cut calories, restrict certain foods and increase our exercise that our body responds by being more hungry and increasing cravings. We try to take extreme measures only to find that we don’t really have a chance at making the weight loss last long term.
Don’t misunderstand; exercise is good for you. There are many benefits to regular exercise such as improved cardiovascular function, increased strength and flexibility, and lowering stress which will lower cortisol but weight loss is not one of the significant benefits of exercise.
So if restricting calories causes are energy usage to slow and results in us being more sedentary outside of the times we exercise or eating more in response to exercise, how do we lose weight and keep it off?
To keep weight off long term, we need to address the underlying hormonal trigger to hunger and appetite; mainly insulin. To lower weight and keep it off, we need to lower our insulin level.
There are two aspects to lowering insulin levels (1) the foods we eat and (2) when we eat and this will be the topic of the next blog.