Lifestyle affects diet, and likewise, diet affects lifestyle. Research that has examined the role of exercise, fat and hormones in controlling appetite provides and explanation for why so many people seem to spiral out of control once they start gaining weight. In short, regular exercise reduces hunger and additional fat increases hunger.
Exercise-Induced Anorexia
Research from the School of Sport, Exercise and Health Sciences at Loughborough University has looked at the role of exercise on the release of hormones that affect hunger.
If you have exercised to lose weight you may have noticed that your appetite does indeed reduce. Often people find that if they exercise in the evening they need to each much less food than normal, sometimes nothing at all. This is one of the reasons why exercise is so important in losing weight.
Exercise-induced anorexia is a phrase used to describe the condition whereby a person that does a lot of cardio exercise has significantly reduced appetite that they simply do not want to eat. As a result they lose more fat due to a greatly increased energy deficit.
Athletes trying to cut fat and people trying to lose weight generally both need to know how exercise affects their body in terms of hormone release as well as fat burning. Many people associate exercise with aiding weight loss by a combination of burning fat when exercising and increasing metabolism as a result of additional muscle tissue.
Often we hear people saying that as soon as they stop exercising all their weight comes back. It seems that this is not only because they are burning less energy, but also because they are eating more as a result of lowered concentrations of hormones that suppress hunger.
Episodic and Tonic Hormones
There a many hormones at play in regulating hunger. Two of the better known ones are grehlin, which increases appetite, and Peptide YY (PYY) which reduces hunger.
We mentioned in the 10 Scientific Ways To Lose Weight that when protein is eaten PYY hormone is released which helps to reduce appetite. A similar release of PYY happens when we exercise. As well as PYY being released the research suggested that glucagon-like peptide 1 was also at play in reducing appetite during and after exercise.
Glucagon is the hormone that is released when blood sugar levels fall. It aids the release of sugars stored in fat cells, so aids the breakdown of fat, which is why a “glucagon-like” peptide could be very useful in helping with weight loss.
The process of “after burn” has been talked about by many people, but never really properly understood. After burn refers to the fact that the body continues to burn fat after exercising. This may be partly due to the increase in the glucagon-like peptides that are aiding the release of sugars from stored energy reserves (fat).
Individual Variations in Response to Exercise
Exercising to reduce appetite is not an option for everyone though, as it seems that there is “individual variability in the response to exercise”. However, what has been found that exercise does not cause an increase in appetite. This is something that many people do get wrong – they exercise and then think that they need to eat more.
“From a practical standpoint athletes should not feel concerned that exercise will cause overeating as there is limited evidence to support this. For those desiring weight loss there may be some merit in performing exercise in the postprandial period as a means of enhancing the satiating effect of a meal but additional evidence is required to confirm the effectiveness of this strategy.”
Postprandial simply means “after eating”. So this conclusive comment suggests that exercising after eating may increase the length of time that you feel full and so curb appetite.
“There is evidence that exercise can have a beneficial influence on appetite and appetite-regulating hormones facilitating a negative energy balance and weight loss…. the wealth of available research and the speed at which knowledge is advancing in this area bring hope that improved strategies for weight control may be on the horizon.” David Stensel
Many people do report eating much less in the evenings when they exercise. If you are trying to lose weight then you should try to add some additional workouts to your week. Have a very light dinner and then exercise about 45 minutes afterwards and note if you feel the need to eat again that evening. You may find that late night snacking is curbed.
Obesity Causes More Hunger
In direct contrast to exercise reducing hunger, obesity, or more specifically an excess of adipose tissue (fat) increases hunger. It seems a little paradoxical, but the more fat that you accumulate, the more hungry you are likely to feel.
In 2010 obesity research carried out by University College London (UCL) revealed that excessive fat deposits blocks hormones that help to control hunger. This is one of the reasons why overweight people find it so hard to stick to a diet – even when they are eating enough food they feel more hunger than healthy people that eat less.
Hunger Killer Hormones PYY and GLP-1
The two hormones that reduce hunger that are affected by high fat deposits are PYY and GLP-1. We have mentioned the role of PYY in our guide to losing weight, as this is the hormone that is released when we digest proteins, which is why eating protein with each meal. especially for breakfast, helps to ward off hunger.
“We know these hormones play a key role in controlling how hungry we feel and how much we eat, but here we’ve shown that obesity itself has a compounding detrimental affect on our hunger hormones which can hamper our dieting efforts. If it’s possible to supplement these hormones we may be able to restore the body’s natural ability to regulate appetite.” Dr Rachel Batterham, UCL.
An increase in the number of fat cells manages to blocks the hormones so that they do not signal the brain that it is time to stop eating. This means that hunger lasts longer, and eating continues even after you have had enough to eat.
It is thought that weight loss could be aided medication that increases the PYY hormone in the blood. However, it is not known at the moment how easy it would be to control PYY levels. If too much floods the system a person my not want to eat at all, and rapid weight loss may occur leading to serious healthy problems.
Weight Loss Surgery Reduces Hunger
An interesting discovery was the bariatric surgery that involves altering the passage of through the gut, leads to an increase in the release of PYY hormones (Peptide YY), so helps to reduce hunger. This means that bariatric surgery aids weight loss in 2 ways:
- By decreasing the absorption of nutrients from food into the blood (less energy taken in)
- By decreasing the feelings of hunger by releasing more PYY hormone
It is not actually known why bariatric surgery leads to more PYY being released.
“The true biological effects of bariatric surgery are still relatively unknown, but if we can learn more about how it impacts the metabolism to achieve such substantial weight loss and improvement in type 2 diabetes, we may be able to develop alternative treatments that do not require invasive surgery.” Dr Rachel Batterham, UCL.
This research provides 2 new tools to help to provide a medical cure for obesity. Obesity is caused when a person consistently consumes too much food. The only way to reverse obesity is to reduce the intake of food, however, many people are unable to exert enough willpower to control their appetite.
Another important conclusion was that if someone experiences a reduction in PYY when dieting this can lead to less weight loss;
“relative PYY deficiency during dieting may compromise weight-loss attempts.”
As PYY is released when protein is consumed, this may go some way to explain why high protein diets such as Atkins and the Dukan diet are generally very successful in the first few months of dieting, and why people often feel very hungry all the time while on low fat (which is often also low protein) diets.
The key to weight loss remains taking in less energy (food) than the body burns (metabolism) each day. The hard part for many people is ignoring their hunger. Understanding the role of hormones and diet can go some way to reduce feelings of hunger, thus helping people to control their appetite to aid weight loss. Also it may be possible to prescribe PYY in the future, which will aid weight loss without the need for surgery.
If you need some help and advice regarding diabetes, visit Diabetes UK and Diabetes Help.
References
“Exercise, Appetite and Appetite-Regulating Hormones: Implications for Food Intake and Weight Control” by David Stensel. Ann Nutr Metab 2010;57 (Suppl. 2):36-42 (DOI: 10.1159/000322702). Full article.
School of Sport, Exercise and Health Sciences, Loughborough University
“Diet and Gastrointestinal Bypass-Induced Weight LossThe Roles of Ghrelin and Peptide YY” by Keval Chandarana, Cigdem Gelegen, Efthimia Karra, Agharul I. Choudhury, Megan E. Drew, Veronique Fauveau, Benoit Viollet, Fabrizio Andreelli, Dominic J. Withers and Rachel L. Batterham. Published online before print February 3, 2011, doi: 10.2337/db10-0566 Diabetes February 3, 2011