How Dieting Makes Us Hungry – Calories Part VIII

By Jason Fung, MD

Click here for Calories Part IPart IIIPart IVPart VPart VI, and Part VII.

Weight Loss

We’ve looked at energy expenditure over the long term. What are some of the hormonal changes that accompany weight loss? For that let’s look at this study:

Long-Term Persistence of Hormonal Adaptations to Weight Loss
N Engl J Med 2011; 365:1597-1604 October 27, 2011 Sumithran P

This study recruited 50 patients who were given liquid shakes (51% carbohydrate). Over the first 10 weeks of the experiment, they received only 500 calories per day. This produced an average weight loss of 13.5 kg. So far, so good.

Next, they were prescribed a diet for weight maintenance based on their measured energy expenditure. Patients were also followed up every 2 months and encouraged to exercise 30 minutes per day. They were given advice to eat low glycemic index carbohydrates and a low fat diet.

Here things didn’t go quite as well. Despite their best intentions, almost half of the weight was regained. On average, 5.5 kg was regained from weeks 10-62.

Hormonal Change

Hormonal analysis was performed on participants at week 0, 10 and 62 after fasting and a standardized meal. What were the results?

The first hormone to look at is ghrelin – the so called hunger hormone. This hormone basically makes us hungry. Patients were more hungry over the initial weight loss phase, but even after 62 weeks, there is a significant increase in the hormone ghrelin. What does that mean? It means that they felt more hungry. The hunger never leaves.

The next hormone to look at is peptide YY. This is a satiety hormone released in response to protein and fat. Essentially, Peptide YY make us feel full. They also analyzed the hormone amylin and cholecystikinin, but the results are similar so I’ve only included the graph for peptide YY.

Again, over the initial weight loss phase, peptide YY was lowered, but even after 62 weeks, Peptide YY (as well as amylin and cholecystikinin) are significantly reduced. What does that mean? That means that in response to a standard meal, the subjects felt less full. This feeling never leaves us.

Hunger and Desire To Eat

These hormonal changes happen almost immediately and persist almost indefinitely. The results on hunger and desire to eat can be seen to the right. Subjects after weight loss felt more hunger and more desire to eat.

We already know that patients on a diet tend to feel more hungry. It turns out that this isn’t some kind of psychological voodoo. What makes us hungry? It is the hormones.

Hunger hormones (ghrelin) were higher and this caused more hunger. Satiety hormones were lower (amylin, peptide YY, and cholecystekinin) and therefore subjects felt less full and had more desire to eat.

Let’s put all this together and think about this from the body’s standpoint. Remember that the body acts as a thermostat with a certain Body Set Weight (BSW).
Suppose our BSW is, for example 200 pounds. We can restrict calories and but leave macronutrient content the same (for example 50% carbs, 30% fat, 20 protein). For a while, we will lose weight – say down to 180 pounds.

However, because the BSW is still 200 pounds, the body will try its damndest to get back up to 200 pounds. It will start almost immediately by trying to get us to increase our caloric intake. It does this by increasing ghrelin and suppressing amylin, peptide YY and cholecystikinin (satiety hormones). This has the effect to make us hungry and increase our desire to eat.

At the same time, this decrease in weight will lead to a decrease in total energy expenditure. The body will start ‘shutting down’ its metabolism. As we saw with the starvation studies – body temperature drops, heart rate drops, blood pressure drops, and heart volume decreases all in a desperate effort to conserve energy.
There are also psychological effects produced, such as obsessive thoughts about food and inability to concentrate.

The end result – weight regain. This, of course, is obvious to anybody who has ever been on a diet.

As you can see, this has nothing, nothing, nothing, NOTHING to do with a lack of willpower or any kind or moral failure. It is simply a hormonal fact of life. We feel hungry, cold, tired and depressed. These are all real, measurable physical effects of calorie restriction.

So here’s the bottom line. By focusing solely on calories and caloric restriction (Caloric Restriction as Primary), we ignore the fact that weight loss in this method will result in the body desperately trying to bring the weight back up to its original weight. We get hungry and the body shuts down metabolism to conserve calories so that we will regain the weight. It is a virtual guarantee.

Virtually all long term studies of dieting (such as the massive Women’s Health Initiative) show weight regain. In fact, I don’t even need to convince you of this fact. You already know in your heart of hearts that it is true.

This, then, is the vicious cycle of under-eating. We start by eating less. We lose some weight. Then our metabolism slows and hunger increases. We start to regain some weight. We now redouble our efforts by eating even less.

A bit more weight comes off, but we again ramp down Energy Expenditure and increase hunger. Weight starts to be regained. This cycle continues until it is intolerable.

At that point, we cannot follow this diet and we go back to our original weight. Friends, family, medical professionals now blame the victim by secretly thinking that it is ‘our fault’ that we could not lose the weight. Somehow, we feel that we are a failure. It happens to all of us – even doctors. Sound familiar? Yeah, I thought so.

Continue to Calories part IX here
Begin here with Calories I
Click here to watch the entire lecture: The Aetiology of Obesity 1/6 – A New Hope

By The Fasting Method

For many health reasons, losing weight is important. It can improve your blood sugars, blood pressure and metabolic health, lowering your risk of heart disease, stroke and cancer. But it’s not easy. That’s where we can help.

Jason Fung, MD

By Jason Fung, MD

Jason Fung, M.D., is a Toronto-based nephrologist (kidney specialist) and a world leading expert in intermittent fasting and low-carb diets.

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