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Study questions ‘calories in, calories out’ equation for body weight

By Caroline Scott-Thomas , 01-Sep-2011

The equation for energy balance and its relationship to body weight may not be as simple as ‘calories in versus calories out’, according to a Lancet paper in the journal’s special series on obesity.

‘Calories in, calories out’ has been a long-standing mantra for many players in the food and beverage industry, particularly when specific foods are singled out for criticism by public health advocates or policy makers. However, US and Australian researchers writing in the latest edition of British journal The Lancet, suggest that the conventional wisdom about weight gain and loss behind this may be overly simplistic.

Using mathematical modeling, the researchers showed that weight loss may slow as a person becomes slimmer – debunking the commonly held belief that cutting about 500 calories a day will result in continuous weight loss of about a pound a week.

“Widespread past use of erroneous rules for estimation of human weight change have led to unrealistic expectations about the potential effect of both behavioral and policy interventions,” the researchers wrote.

On the basis of their simulation model, they gave an approximate rule of thumb for an average overweight adult: Every change of energy intake of 100kJ (24 calories) will lead to an eventual bodyweight change of about 1 kg (2.2lb). And the change slows significantly over time: About half of that weight change would be achieved in about a year, and about 95% within about three years.

However, differing body compositions at the beginning of the weight loss period may also play a role in how quickly an individual would lose weight, even with the same change in energy intake.

“We have shown how inter-individual weight-loss variability resulting from the same intervention can be caused by differences in the initial body composition between individuals as well as the uncertainty about the baseline energy expenditure,” the researchers wrote.

“We also showed that the timescale of human weight change is long and depends on the initial body composition. Furthermore, changes of energy intake can theoretically result in different weight changes compared with initially energy-equivalent changes of physical activity expenditure.”

The Lancet series on obesity can be accessed here . Free registration is required.

Source: The Lancet

Vol. 378, Iss. 9793, pp 826 – 837 doi:10.1016/S0140-6736(11)60812-X

“Quantification of the effect of energy imbalance on bodyweight”

Authors: Kevin D Hall, Gary Sacks, Dhruva Chandramohan, Carson C Chow, Y Claire Wang, Steven Gortmaker, Boyd A Swinburn

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