Obesity Weekly

A weekly update about some aspect of Obesity. Published Monday mornings

Archive for March 23rd, 2009

Diet or Diet and Exercise?

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Ideally any weight loss plan would incorporate both diet and exercise. However, the latter seems to be more difficult to implement and maintain.  Exercise takes time and effort while dieting is a modification of a daily behavior. A reason to incorporate both diet and exercise is that by decreasing calories intake and increasing calorie expenditure a quicker weight loss can be achieved.  Because, everyone knows, that calories in and calories out work like a balance right?  Decrease calories consumed and the weight will start to come off, right?  Well only for a while. Our bodies adapt to different calorie and fitness levels based on what we do and what we eat.  We will explore why the simple balance model is too simplistic to explain some of the challenges that lie in battling weight.

A recently published study by the Pennington Biomedical Research Center demonstrates important differences in diet and diet plus exercise that explain why it is difficult to maintain weight loss using just diet alone (1).  (These results are published on the Public Library of Science Online site.  It is an open access site, so if you want to download and read the paper in detail you can.)  The study tested the effects of calorie restriction (CR), calorie restriction and exercise (CR+EX), a low calorie diet (LC) compared with a control group (2).  The CR group consisted of decreasing calorie intake to 75% of what is required calculated from the subjects baseline energy requirement (a 25% reduction).  The CR+EX group had a 25% change from meeting the daily energy requirements, but 12.5% consisted of a decrease in calories, while exercise was added to increase calorie burn 12.5%.  The LC group subsisted on 890 Calories (3) per day until a 15% reduction in weight was achieved.  The CR and CR+EX groups had individual diets prepared for them for part of the time (3 months) and they were trained to adhere to the same type of diet while feeding themselves (months 3-6).  The diet consisted of 30% calories from fat, 15% from protein and 55% carbohydrate, so no special restrictions on nutrients were employed.  The study lasted for 6 months and changes in body composition and energy expenditure were assessed at baseline, month 3 and month 6. They were able to calculate total energy expenditure in the subjects using a whole room calorimeter and doubly-labeled water.  The latter method permits the measurement of energy expenditure in free-range humans and a more accurate assessment of real life energy expenditure.  Fat mass and fat free mass were also measured using a whole body imaging method called DEXA scanning. There were a total of 48 individuals, 21 males and 27 females, who were overweight (BMI>25) but were not obese (BMI<30) who started the study and only 2 of the subjects failed to complete the study. 1 was in the control group and 1 was in the LC group.

At month 3 and month 6 all intervention groups achieved significant reductions in weight, both in fat mass and fat free mass. The loss of fat free mass was slightly less for the exercise group, but it was a decrease none the less.   The LC group lost the most weight, (you try living on 890 Calories per day) about 24 pounds, which for an overweight, but not obese person would almost certainly take them into a normal BMI range.  The interesting results from this study were demonstrated when energy expenditure was measured.  Both the CR and the LC groups had a decrease in total daily energy expenditure of more than 10% at both 3 months and 6 months.  No decrease in daily energy expenditure was observed in the exercise group. The decrease in energy expenditure was explained by two main factors: 1) metabolic adaptation to decrease energy expenditure in an environment with fewer calories available and 2) a decrease in spontaneous physical activity.  That means that your body slows down to try and conserve and you unconsciously move less.  So if you are trying to loose weight, the last thing you want to happen is to have your body slow its metabolic rate and for you to move less during the day.  The addition of exercise prevented both changes. This has important implications for losing and maintaining weight loss.  Remember at the beginning I said that the simple balance model was too simple?  Well this demonstrates one aspect.  If you just try to diet, your body will fight back (as if you didn’t know that already) and slow itself down.  One way to prevent this adaptation is to make your body work.

So what do all these numbers and percentages mean for an individual?  I am going to calculate some of the study results for two hypothetical individuals, average Joe and average Joelle.  Lets say Joe is 6 ft and weighs 220 pounds.  He needs 2600 Cal/day to maintain his weight.  He has a BMI of 29.8% and a body fat percentage of 25%.  On the CR plan, Joe would consume 1950 Cal/day and weigh 207 pounds at month 3 and 201 pounds at month 6. His ending BMI would be 27.3 and body fat percentage would be 20.8%.  However, his metabolism would slow between 300-400 Calories per day.  That would be the equivalent of 1 hour of normal pace walking per day.  On the CR+EX plan, Joe would consume about 2300 Cal/day and his weights would be about the same at month 3 and 6.  However, his ending body fat % would be 20.1%, or 0.7% less fat than with just diet alone.  And no decrease in basal energy expenditure would occur.  He would be exercising just over 300 Calories per day, or about an hour of normal pace walking.  He could also run 3 miles in 30 minutes and burn about the same amount.

How about Joelle?  She is 5ft 6in and weighs 180 pounds.  She needs 1900 Cal/d to maintain his weight.  She has a BMI of 29.0% and a body fat percentage of 37.6%.  On the CR plan, Joelle would consume 1425 Cal/day and weigh 167 pounds at month 3 and 161 pounds at month 6. Her ending BMI would be 26 and her percentage of body fat would be 34.0%.  However, her metabolism would slow between 200-300 Calories per day, just on diet alone.  Again, the equivalent of 1 hour of normal pace walking per day.  On the CR+EX plan, Joelle would consume about 1650 Cal/day and weights would be about the same.  However, her ending body fat % would be 33.2%, or 0.8% less fat than with just diet alone with no decrease in basal energy expenditure.  She would be exercising just over 230 Calories per day, or about an hour of normal pace walking.  She could also run 3 miles in 30 minutes and burn about the same amount.

So with a little exercise you can prevent your body from decreasing its basal metabolic rate, burn a bit more fat and be able to get the same amount of weight loss while maintaining a slight calorie restriction.


1. http://www.plosone.org/article/info:doi/10.1371/journal.pone.0004377

2.  The statistical analysis of the study also combined the data from the CR and LC group, but in my opinion this unnecessarily complicated the analysis without adding any additional scientific insights.  I think the reason was to achieve significance in the total daily energy expenditure not explained by changes in fat free mass and fat mass at month 6 (Table 2, last column).  The CR and LC group are essentially diet alone groups but the daily caloric intake was different.  The CR group was a 25% reduction for each individual while the LC group was 890 Cal per day which was almost certainly more than a 25% reduction.

3.  In the paper, kcals are used.  One diet Calorie equals 1000 calories (or 1 kcal) from a chemistry/science perspective.  Diet Calories are typically written with a capital “C”, but since this is a peer-reviewed scientific paper, most journals require the use of standard units, so kcals are used and kilograms are used for weight.

Image from: http://www.fat2fitradio.com/wp-content/uploads/2008/10/1177970407-energy-balance.jpg

Written by ecable

March 23, 2009 at 5:00 am

Posted in 5755, Exercise, Health