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Diet and Exercise to Lose Weight

We looked at three well conducted trials on diet in Diet Therapy for Weight Loss, each of which showed modest weight loss over the longer term. So what about exercise to lose weight, or even the combination of diet and exercise to lose weight - can changes to the classic causes of obesity be used to reverse things?

Exercise to Lose Weight

There have been many trials published which looked at exercise to lose weight and to reduce the amount of abdominal fat (love handles, beer belly, belly fat, muffin top – the list of alternatives is almost endless) as measured by waist circumference.

A review1 of these articles was reported in 2006 which summarized 43 studies involving 3476 participants. This review reveals strong evidence that physical activity alone, i.e., aerobic exercise, in obese and overweight adults results in only modest weight loss. The key results were:

• When compared with no treatment controls (for comparison), exercise resulted in small weight losses across a combination of studies (mean weight difference between the two 2.0Kg; Note: this is not actual weight loss, it is the difference).
• Exercise combined with diet resulted in a greater weight reduction than diet alone (mean weight difference between the two -1.1 kg).
• Increasing exercise intensity increased the magnitude of weight loss (mean weight difference between the two -1.5 kg).

In one of the studies2, those participants, both male and female, who were part of an exercise only group saw their average weight decline by 0.5Kg over 1 year. The control group (a general group of participants who changed nothing, but are recorded as a comparison) saw weight increases of 0.65Kg. So the mean weight difference between the two was 1.15Kg in this particular study.

Interestingly, the exercise group saw their calorie intake increase slightly relative to the control group. A similar effect has been obseved more recently, whereby a study confirmed that even the thought of exercise or the mention of similar phraseolgy increased peoples’s calorie intake3.

Diet and Exercise to Lose Weight

Remember those three studies into the longer term effects of popular diets we discussed in Diet Therapy for Weight Loss? Well each of those three studies incorporated exercise into their plans, so those results actually indicate the combined results of diet and exercise for weight loss. Unfortunately, all of these trials did not report on the exercise outcomes.

Study 1

The study which compared Ornish, Atkins, Zone and Weight Watchers diet programs4, followed the exercise levels according to each participant’s own reporting (vigorous, moderate, mild, minimal). All participants were encouraged to obtain at least 60 minutes of exercise weekly. They found at one year that the level of activity modestly increased among all groups, according to the table shown:

physical activity changes throughout study 1

The researchers concluded that:

• After accounting for dietary adherence, there was no significant association between change in exercise and change in body weight.
• A variety of popular diets can reduce weight under realistic clinical conditions, but only for the minority of individuals who can sustain a high dietary adherence level.

Study 2

In study 2, which examined the low-fat diet, the Mediterranean diet and the low-carb diet5, the physical-activity level for each participant was converted into a metabolic equivalents per week score6.

The amount of physical activity increased significantly from baseline in all groups, with no significant difference among groups in the amount of increase. See table:

 physical activity changes throughout study 2

Study 3

In study three which examined the diets with different compositions of fat, protein and carb7, the goal for physical activity was 90 minutes of moderate exercise (eg. walking) per week. Participation in exercise was monitored by questionnaire and an online self-monitoring tool.

Unfortunately, the results were not reported.

Diet, Exercise and Waist Circumference

All three trials we have looked at, whilst testing the effect of popular diets on weight loss, also had measures of abdominal fat as assessed by measurement of waist circumference.

Study 1

In study 1, waist circumference data was recorded at the naval4.

Weight reductions were highly associated with waist size reductions for all diets at 1 year, with no significant difference between diets.

In women, mean waist size decreased by 2.3 cm, and

In men waist size decreased by 3.1 cm at 1 year.

Study 2

Waist circumference was measured halfway between the last rib and the iliac crest in study 25.

All groups had significant decreases in waist circumference, but the differences among the groups were not significant. The waist circumference decreased by a mean of 2.8 cm in the low-fat group, 3.5 cm in the Mediterranean-diet group, and 3.8 cm in the low-carbohydrate group.

Study 3

In study 3, the method for measuring waist circumference was not recorded7.

The change in waist circumference did not differ significantly among the diet groups.

For those participants within the groups who submitted their waist circumference data, the greatest reduction in waist circumference occurred at 12 months (around 7 to 8 cm drop from baseline), with participants on average reducing waist circumferences by around 6 cm by the end of the 2 years.

Bottom Line

From these studies we can conclude that exercise alone only results in small changes in body weight.

When combined with dietary therapy, the results are improved, but in some studies the extent of improvement did not change significantly with increased intensity of exercise.

The studies indicate that a reduction in weight from diet and exercise is associated with a reduction in abdominal fat as measured by waist circumference.

For successful, significant weight loss and sustained weight maintenance, more is needed than exercise and diet therapy.

This additional requirement brings us to the tripartite approach, commonly referred to as Lifestyle Choices, of Diet, Exercise and Behavioural Therapy for Successful Weight Loss.

Sources:

1. Shaw KA, Gennat HC, O'Rourke P, Del Mar C. Exercise for overweight or obesity. Cochrane Database Syst Rev. 2006 Oct 18;(4):CD003817. PMID: 17054187. Full text.

2. Stefanick ML, Mackey S, Sheehan M, et al. Effects of the NCEP Step 2 diet and exercise on lipoprotein in postmenopausal women and men with low HDL-cholesterol and high LDL-cholesterol. New Engl J Med 1998;339:12-20. PMID: 9647874. Full text.

3. Albarracin D, Wang W, Leeper J. Immediate Increase in Food Intake Following Exercise Messages. Obesity (Silver Spring). 2009 Feb 26. [Epub ahead of print]. PMID: 19247284. Free full text not available.

4. Dansinger ML, Gleason JA, Griffith JL, et al. Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial. JAMA. Jan 5 2005;293(1):43-53. PMID: 15632335. Full text.

5. Shai I, Schwarzfuchs D, Henkin Y, et al. Weight Loss with a Low-Carbohydrate, Mediterranean, or Low-Fat Diet. N Engl J Med. 2008 Jul 17;359(3):229-41. PMID: 18635428. Full text.

6. Ainsworth BE, Haskell WL, Whitt MC, et al. Compendium of physical activities: an update of activity codes and MET intensities. Med Sci Sports Exerc 2000;32:9 Suppl:S498-S504. PMID: 10993420. Free full text not available.

7. Sacks FM, Bray GA, Carey VJ, et al. Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. N Engl J Med. 2009 Feb 26;360(9):859-73. PMID: 19246357. Full text.

 

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