Junkfood Science: Missing evidence or... They really do just make stuff up!

August 10, 2008

Missing evidence or... They really do just make stuff up!

Last week, fat women were being advised to exercise 55 minutes a day to lose weight and keep it off, even though the study being reported had found that no amount or intensity of exercise worked to maintain weight loss. Today, new public health guidelines have stepped it up, calling for 1 ½ hours a day of moderate-vigorous exercise, as well as two weight training sessions a week, for all overweight adults.

It’s all part of the Scottish Government’s efforts to eradicate obesity. According to NHS Health Scotland, the new health policy is based on guidelines from the American College of Sports Medicine for weight loss and maintenance.

It would appear, however, that no one actually read the ACSM position paper because the expert authors could find no evidence to support recommendations of exercise for weight control.

As Scotland On Sunday reports:

1½ hour workout 'is only way to beat flab'

[O]verweight Scots will need a daily 90-minute workout to stand any chance of fighting the flab, according to new public health guidance. The advice, which GPs and nurses are to pass on to NHS patients, also warns that light housework such as cleaning or dusting, or strolling round the supermarket, must not be counted in the daily exercise regime. Instead, only "moderate" or "vigorous" activity such as brisk walking, running, swimming and heavy domestic chores like vacuuming, mowing the lawn or painting and decorating count. And as part of their weekly regime all adults should perform two sessions of weight training exercises.

The updated guidance on exercise targets has been published by the Scottish Government's public health advisory body NHS Health Scotland. But though it has been welcomed by some experts, others have dismissed it as "dictatorial and inappropriate", and unrealistic for many busy professionals. The guidance document, 'Energising Lives', states that NHS staff must make physical activity a "higher priority", with 60% of men and 70% of women not thought to be taking enough exercise...

In a press statement issued last night, a spokeswoman for NHS Health Scotland said the document was based on internationally recognized guidelines produced by the American College of Sports Medicine. The official ACSM position paper and recommendations, “Appropriate Intervention Strategies for Weight Loss and Prevention of Weight Regain for Adults,” were published in the official journal of the ACSM.

Actually reading it, however, surprisingly reveals that the body of research evidence is totally different from what even we’ve been led to believe and what might seem intuitively correct. In fact, as the ACSM systematically examined the evidence behind each of the popularly believed ideas about exercise, it found more myths than facts.

Exercise for weight loss?

The lead author of the ACSM position paper was John M. Jakicic, Ph.D., associate professor and Director of the Physical Activity and Weight Management Research Center at the University of Pittsburgh. The white paper began by reporting that, according to the body of evidence, exercise has little effect on weight loss. Transient and short-term weight loss reported in the medical literature was primarily related to caloric restrictions. As it summarized:

There is little evidence that suggests that exercise alone produces magnitudes of weight loss that are similar to what can be achieved with dietary modification.

So if exercise alone doesn’t seem to work, the ACSM then examined how about exercising longer?

The ACSM position paper found few studies examining the duration of exercise and weight. Of the three studies, the longest was the 18-month results of research on fat women using home treadmills, led by professor Jakicic. Professor Jakicic’s research was just reviewed last week here, and had found no amount or intensity of exercise had worked to maintain weight loss over two years, and that the temporary weight loss had most corresponded to the severest caloric restrictions.

So if exercising longer doesn’t work, the ACSM paper then examined how about exercising harder?

The ACSM position paper found:

There have been few studies that have adequately examined the impact of various intensities of exercise on weight loss. Duncan et al. attempted to maintain total volume of exercise while manipulating intensity in a 24-wk study of overweight women. The results of this study showed that the intensity of exercise... did not result in differential effects on body weight or body composition after 24 wk of treatment.

So if exercising harder doesn’t work, the ACSM paper then examined how about an “active lifestyle” and accumulating more intermittent exercise throughout the day?

The ACSM position paper exposed that the U.S. CDC and ACSM had had no evidence when they issued their recommendations for accumulating at least 30 minutes of moderate-intense activity each day to help promote weight loss. Where were the headlines? And, to this date, there is no evidence. As the position paper reported:

There have been a few studies that have examined the effectiveness of intermittent exercise in weight loss programs. Intermittent exercise has typically been defined as accumulation of 30–40 min of exercise per day through participation in multiple 10- to 15-min exercise sessions daily... the Centers for Disease Control and Prevention and the American College of Sports Medicine recommend[ed] the “accumulation” of at least 30 min of moderate intensity activity per day, yet at the time of this recommendation, there was no evidence that this would be an effective strategy for overweight adults seeking weight loss.

Donnelly and colleagues compared continuous and intermittent exercise, with no dietary intervention, over a period of 18 months and showed no change in body weight following treatment.

So if accumulating physical activity throughout the day doesn’t work, how about adding resistance, muscle-building exercises?

Even while eating starvation-level calories in clinical studies, resistance exercise had no effect on weight loss, according to the ACSM:

[W]hen resistance exercise is combined with dietary energy restriction, there appears to be little benefit in terms of absolute weight loss. These results have been consistent across studies with energy intakes as low as 800 kcal/d or as high as approximately 1300 kcal/day. In one of the few long-term studies (40 week) to date, Wadden et al. have shown that resistance exercise alone or in combination with endurance exercise did not enhance weight loss compared with endurance exercise alone in a behavioral weight loss program, with all groups prescribed a diet ranging from 900 to 1250 kcal/day.

But what about building and preserving muscles to help burn more calories?

What may be another surprise is that they could find no support in clinical trials for the popular belief that muscles can help prevent the normal reductions in metabolism that accompanies calorie restrictions as the body attempts to conserve calories and preserve its size:

Data may suggest that preserving FFM [muscle] will prevent declines in resting energy expenditure [calorie burning] that are often observed with weight loss. However, intervention studies do not support this belief, with the majority of studies showing that resistance training does not prevent the decline in REE that occurs with diet-induced weight loss.

For example, Kraemer and colleagues combined a periodized resistance-training program with an endurance exercise component and dietary modification. The addition of resistance exercise did not improve weight loss or blunt decreases in REE compared with diet combined with endurance exercise or the diet only condition. Moreover, the addition of resistance exercise to endurance exercise and diet modification did not minimize the loss of FFM compared with endurance exercise combined with dietary modification or dietary modification alone.

In other words, the ACSM could find no clinical evidence to support exercise prescriptions as “appropriate intervention strategies for weight loss and prevention of weight regain.”

So what were its recommendations for Americans and issued through our CDC?

It is recommended that overweight and obese individuals progressively increase to a minimum of 150 min of moderate intensity physical activity per week, as this level of exercise may have a positive impact on health in overweight and obese adults. However, for long-term weight loss, overweight and obese adults should eventually progress to higher amounts of exercise (e.g., 200–300 min/week of leisure-time physical activity...) It is recommended that resistance exercise supplement the endurance exercise program in overweight and obese adults.

And you believe that our government health guidelines are based on something like... evidence?

So, when fat people are instructed by their doctors to exercise — another weight loss intervention lacking in evidence — and they don’t lose weight, they will invariably be blamed. And, once again, fat people will be wrongly seen as noncompliant or irresponsible, lazy or slothful.

© 2008 Sandy Szwarc

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