The Relationship Between Exercise and Diet

Athletic woman preparing foodSometimes people really do like to complicate matters. There is already enough confusion regarding weight loss, which leads to many people making costly weight loss mistakes.

In recent years two pieces of research were published which really helped to confuse matters.

One study concluded that exercise does not help you to lose weight while the other concluded that diet does not help you to lose weight either. So neither work!

Well, let’s try to bring some sanity back to the relatively simple task of reducing body fat.

Exercise Alone Does Not Help You Lose Weight

The British Journal of Sports Medicine published a report which concluded that exercise fails to help many people lose weight. A team of sports scientists conducted a study which involved monitoring the calorie expenditure of a group of people on a rest day and then again on a controlled exercise day.

The results showed that exercising did not generate a calorie “after burn” that many people believe. In fact, in some cases people burned less fat on their exercise days than on their rest days.

In the study all the subjects were overweight or obese, and the study only monitored progress over a short period. From practical experience we see that although in the very short-term people do not lose weight when they start exercising, on the longer term they do.

For example, when people start jogging / running they often see no or little weight reduction in the first month. It is only in the second month of running when the body has become stronger and fitter that a person can push themselves hard enough to burn off enough extra calories to make a real difference.

Short Term Weight Loss is Not Possible

In the average 45 minute cardio session the number of calories burned is about the same as that for a sports energy drink, and less than that of a protein / carbohydrate replacement drink.

So it stands to reason that without strictly controlling calorie intake weight loss is much harder to obtain. In fact the study showed that weight loss was not possible in the very short-term by exercise alone.

Another reason why people fail to lose weight is because they gain more muscle when they start exercising. Although there is no weight loss, there is sometimes some fat loss, which is the ultimate goal. Muscle is healthy, fat is not.

Diet Without Exercise Does Not Aid Weight Loss

The second study that was published in the American Journal of Physiology concluded that diet without exercise does not aid weight loss.

The scientific community has once again thrown our understanding of health and fitness upside down. However, we have to listen to our scientists as they are the experts!

In this study it was concluded that eating fewer calories does not contribute a great deal to achieving weight loss goals and that eating healthy food, instead of unhealthy, does not directly aid weight loss either.

This is the sort of conclusion that leads tabloid readers reaching for the donuts and pizza!

Explanation of the Research

The research group from the Oregon Health and Science University suggested that the reason diet does not always lead to aid weight loss was because when people eat less they become less active, therefore burning fewer calories, so the reduction in calories eaten does not lead to a calorie deficit because the body needs less.

“This research shows that simply dieting will not likely cause substantial weight loss. Instead, diet and exercise must be combined to achieve this goal.” Dr. Judy Cameron, senior scientist at Oregon Health and Science University.

The research was carried out on primates (18 female rhesus macaque monkeys). After being fed well for several years they were placed on a low-fat and low-calorie diet with 30% fewer calories than they normally ate.

During the first month of their diet their weight hardly changed, with no significant weight loss.

What was surprising was that the monkeys became much less active. They became lethargic and sedentary to conserve energy. In the second month of the study calories were reduced again and this resulted in activity decreasing even further.

As part of this research another group of monkeys were given a standard diet and exercised for one hour per day. These monkeys lost weight.

This study demonstrates that there is a natural body mechanism which conserves energy in response to a reduction in calories.” Dr Cameron, Oregon Health and Science University.

The key to fast and successful weight loss seems to be as it always has been – a combination of healthy diet with fewer calories and regular rigorous exercise!

But Humans Are Not Monkeys!

One thing to consider though, when we make an effort to lose weight by restricting calories, we often do not have the luxury of being able to become less active like the monkeys in the study could – we still have to work and carry out our chores.

So for many people reducing calories is a good way to lose weight.

If you go on a calorie restrictive diet and maintain your activity levels, then you will certainly lose weight, although you need to be sure that you do not become more restful after workouts.

If you decide to just exercise more, the chances are that you will be eating less and eating meals that help with your exercise, i.e. meals that are lower in carbohydrates, less stodgy/easier to digest. These types of food will also help you to lose weight.


“A rapidly occurring compensatory decrease in physical activity counteracts diet-induced weight loss in female monkeys” by Elinor L. Sullivan and Judy L. Cameron. American Journal of Physiology Regul Integr Comp Physiol 298: R1068-R1074, 2010. First published January 13, 2010; doi:10.1152/ajpregu.00617.2009

Beneficial effects of exercise: shifting the focus from body weight to other markers of health” by Neil King, Mark Hopkins, Phillipa Caudwell, James Stubbs, John Blundell. British Journal of Sports Medicine. Published Online First: 29 September 2009. doi:10.1136/bjsm.2009.065557

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