Welcome to part four of The science behind weight loss, a Conversation series in which we separate the myths about dieting from the realities of exercise and nutrition. Here, Deakin University Public Health Research Fellow, Gary Sacks, explains how a new online tool can help users estimate their weight loss, based on their diet and activity:
As governments around the world struggle to tackle rising obesity levels, many people are also fighting their own personal battles to lose weight.
A recent Lancet article I contributed to sheds light on popular myths about weight loss and helps explain what really happens to our bodies when we’re trying to lose weight.
Weight loss myth
There’s a common myth about the amount of weight that can be lost from a reduction in energy intake (calories).
For decades, a high proportion of doctors and dietitians worked on the incorrect assumption that cutting 2100 kJ (about 500 calories) of energy intake every day would result in steady weight loss of about half a kilogram a week.
But this assumption ignores adjustments in the body that take place in response to any change in weight.
What actually happens is that the body’s composition and metabolic rate change after the initial loss of weight, and this leads to a plateau in weight loss.
The use of this incorrect dieting rule leads to unrealistic expectations for diet plans and may help explain why even resolute dieters often fail to reach their target weight.
Typical patterns of weight loss
New research, led by researchers based at the National Institutes of Health (NIH) in the United States, has led to more accurate calculations of how much weight someone can be expected to lose in response to changes in energy intake or physical activity.
The rough dieting rule for a typical overweight adult is that a change of energy intake of 100 kJ per day will lead to an eventual body weight change of about one kilogram, with half of that occurring in the first year.