The science behind weight loss: separating facts from fiction

The science behind weight loss, is part one of a series of sage and sane scientifically-based articles that looks at obesity and separates the myths about dieting from the realities of exercise and nutrition posted on The Conversation, is a website-based independent source of information, analysis and commentary from the university and research sector in Australia. This first installment explains how diets draw you in, but can’t deliver.

Let’s start with a few facts. Australians’ waistbands have increased over the past three decades, with recent data showing 68% of men, 55% of women and 25% of children are overweight or obese.

Excess body fat is a problem for the individual. And it’s ultimately a problem for society because it overloads the national health budget.

Health problems due to excess body fat include an increased risk of type 2 diabetes, coronary heart disease, high blood pressure, asthma, sleep apnoea, musculoskeletal conditions (including osteoarthritis) and certain types of cancer (especially colorectal and breast cancer in post-menopausal women).

There is good evidence to show genes play a role in obesity and explain why some people gain more weight than others when their energy intake exceeds their body’s needs. But genetic factors can’t explain the rapid increase in excess body fat over the past 20 to 30 years.

So what has changed? Two obvious factors stand out.

Physical activity has decreased as we have embraced labour-saving devices and sedentary behaviours. Changes in urban design and the use of cars for transport also play major roles.

An increased reliance on cars means we’re not getting enough incidental exercise.

What we eat and drink has also changed. We eat more. We snack more often. We quench our thirst with sweetened beverages. Portion sizes for drinks, meals and snacks have all increased and foods and drinks that were once kept for special occasions are now daily “treats”.

In spite of calculations showing that our increased food intake and decreased exercise output have increased our national girth, we continue to ignore such obvious factors.

Instead we look for a magic bullet cure-all, with diets high on the list of possible saviours.

The need to consume less is generally an unwelcome message to individuals and to the corporate world, where the “economy” we worship depends on continued increases in consumption. Anything that might decrease consumption of any food or drink is strenuously opposed by those whose profits depend on market growth.

Diets and diet products are also money spinners. Diet books that target a specific scapegoat are also supported by companies who cash in with new product formulations to fit.

Diet books make endless promises about easy ways to lose weight. Flickr/coconut wireless

When health authorities suggested cutting kilojoules by eating less fat in the 80s and 90s, the food industry responded with literally hundreds of low-fat products, which replaced fat with sugars and refined starches.

When this move failed and was replaced by a low carb craze in the 2000s, a flood of low carb products followed.

Some diets proudly proclaim you can eat as much butter and cream as you like, but then forbid almost everything you might have with these items. But there’s a limit to the number of fatty chops topped with butter that most people could eat.

Many people also like the rigidity of a diet’s rules – at least for a few weeks. After that, the rules are gradually broken.

We saw this with the CSIRO’s diets. After 12 months, those on low protein diets increased their protein intake to normal levels, while those on high protein diets reduced their protein intake.

Long term, no diet has proved effective. After the initial weight loss, most people on any diet regain most of what they lost. There’s no mystery to this…..

The Conversation: Read more

Part Two: Want to set up a weight loss scam? Here’s how…
Part Three: Feel manipulated? Anxious? Tune out the hype and learn to love your body
Part Four: Food v exercise: What makes the biggest difference in weight loss?
Part Five: An online tool to help achieve your weight-loss goal (no, it’s not a fad diet)
Part Six: Ignore the hype, real women don’t ‘bounce back’ to their pre-pregnant shape
Part Seven: Quick and easy, or painful and risky? The truth about liposuction
Part Eight: Weight loss and the brain: why it’s difficult to control our expanding waistlines
Part Nine: Are diet pills the silver bullet for obesity?
Part Ten: Want to try the latest fad diet? Just ask your local pharmacist