Science functions best when it is free from any bias or conflict of interest. All those engaged in the process should value what is actually true more than anything else. Unfortunately, there are many sources of bias in science.

Researchers may want their pet theory to be supported. Journal editors want to publish research that will have a high impact. And of course, corporations would prefer that the results of scientific research favor their products and services. A recent round of editorials accuses the Coca-Cola company of trying to put its thumb on the scale of science in order to deflect attention away from sugary drinks as a source of obesity and overweight. What are they doing and what does the science actually say?

Promoting uncertainty

According to The New York Times:

The beverage giant has teamed up with influential scientists who are advancing this message in medical journals, at conferences and through social media. To help the scientists get the word out, Coke has provided financial and logistical support to a new nonprofit organization called the Global Energy Balance Network, which promotes the argument that weight-conscious Americans are overly fixated on how much they eat and drink while not paying enough attention to exercise.

This is one subtle way for corporations to influence science. They find legitimate scientists who already support a position that is favorable to their company and they fund them. This is often not difficult to do, there is often a range of opinions on scientific topics, or at least a minority opinion. You could probably find a scientist to support almost any position.

Give that scientist money to further their research, or to communicate their position to the world, and you may help them promote that position. At the very least you can give the public a distorted view of what the consensus of scientific opinion is, by amplifying a minority voice.

In this way the company can be completely hands off the research and the message. They can honestly say that the opinions are those of the scientist, without their influence. All they are doing is cherry picking the opinions they like. This sort of funding bias is also difficult to regulate. What we can do, and what is being done, is to require absolute transparency when it comes to funding sources.

Diet vs exercise

At the heart of this particular debate is the relative role of diet vs exercise in maintaining a healthy weight. There is some legitimate controversy over this question – are Americans, for example, increasing in weight because we are consuming more or moving less? Should we blame computers and multi-media, or supersized fast food?

As with many such debates (but not all), the answer is somewhere between the two extremes. There is no serious debate about the importance of calorie control in managing weight. There is also a strong consensus that exercise has many benefits to health, and does contribute to maintaining muscle and reducing adipose tissue (fat). The old advice to eat right and exercise regularly still holds.

The real question is the relative importance of each of these factors. If your goal is to reduce excess weight, exercise is helpful but exercise alone (without calorie control) is not very effective. A 2010 study randomized obese women to two groups, one with added exercise the other without, and both groups instructed not to change their diet. They found:

Women in the exercise group exercised a mean of 3.6 days (s.d.=1.3) per week and 178.5 min (s.d.=76.1) per week. Changes in all measures of adiposity favored exercisers relative to controls (P<0.001). The mean difference between groups was: −1.8 kg for body weight; −2.0 kg for total body fat; −14.9 cm2 for intra-abdominal fat area; and −24.1 cm2for subcutaneous abdominal fat area. A linear trend of greater body fat loss with increasing volume of exercise was also observed.

While exercise did result in weight loss, you will notice that 178.5 minutes of exercise per week over a year led to a loss of 2 kg of body fat. That is a lot of work for a small benefit.

What about diets for weight loss? A recent meta-analysis showed that for all diet types, over a year, average weight loss of study subjects was 7.25 kg. That is still modest, especially for someone who is obese, but it is more than the exercise-alone group. There is evidence that more exercise will produce higher weight loss, but there are practical limits to what most people can do.

Some researchers also emphasize that weight is not necessarily the most important measure of health. Metabolic health may be more important. Exercise improves metabolic health, and therefore there are health benefits to regular exercise even if it does not result in significant weight loss.

Also, another issue is not just weight loss but maintaining a healthy weight. Most people who lose weight will gain it back, and then some. Dieting alone is a frustratingly ineffective method for maintaining a healthy weight. A survey of those who were successful show:

National Weight Control Registry members have lost an average of 33 kg and maintained the loss for more than 5 y. To maintain their weight loss, members report engaging in high levels of physical activity (≈1 h/d), eating a low-calorie, low-fat diet, eating breakfast regularly, self-monitoring weight, and maintaining a consistent eating pattern across weekdays and weekends.

So again we are back to a combination of diet and exercise. What about the role of sugar-sweetened beverages (SSB)? A 2006 review concluded:

The weight of epidemiologic and experimental evidence indicates that a greater consumption of SSBs is associated with weight gain and obesity. Although more research is needed, sufficient evidence exists for public health strategies to discourage consumption of sugary drinks as part of a healthy lifestyle.

A 2013 review concluded:

Taken together, the evidence that decreasing SSBs will decrease the risk of obesity and related diseases such as T2D is compelling.

Conclusion: Diet and exercise

There certainly remains some scientific controversy over the exact role of diet vs exercise in maintaining a healthy weight, and the exact role of sugary drinks. This is partly due to the fact that the science is complex, the variables are many and they are difficult to control. It is difficult to do research on the behaviors of people over long periods of time.

Given these challenges, there appear to be several strong signals in the data. Both diet and exercise are important to health in general and specifically to maintaining a healthy weight, metabolic profile, and body composition. When it comes to weight, caloric intake appears to be a stronger factor in the short term, but exercise may be critical to maintaining weight control in the long term. Sugar-sweetened drinks contain significant calories that, if consumed regularly, contribute to overall caloric intake and obesity and overweight.

There is certainly no justification for downplaying the role of calories in general or sugar-sweetened drinks specifically in weight and overall health.


Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.