Consumption of the flavour enhancer monosodium glutamate (MSG) may increase the risk of gaining weight, regardless of energy intake, suggests a new study.
The risk of being overweight – having a body mass index (BMI) of 25 kg per sq. m – was increased by 175 per cent in people with a high intake of MSG, according to findings from a cross-sectional study published in the Nature journal Obesity.
“Animal studies have indicated for years that MSG might be associated with weight gain,” said lead researcher Ka He, MD, from the University Of North Carolina School Of Public Health. “Ours is the first study to show a link between MSG use and weight in humans.”
However, the study findings have been challenged by industry. “This study has no practical significance,” said Brendan Naulty, president of the Glutamate Association, a trade association for manufacturers, and processed food users of glutamic acid and its salts.
Naulty said that, based on World Health Organization (WHO) data, countries with high intakes of the flavour enhancer do not have high population BMI.
“Second, human studies where MSG was added to the diet have failed to show changes in body weight. And third, a recently published rat study suggests that MSG in the diet actually suppresses body weight,” he added.
In the introduction to their paper, however, He and co-workers cite other animal studies that report an induction of lesions in the hypothalamus region of the brain, in addition to leptin resistance, both of which could influence energy balance and promote weight gain.
He and co-workers recruited 752 healthy Chinese volunteers (366 women), aged between 40 and 59, and measured their use of MSG. The volunteers all prepared their food at home and did not consume commercially processed foods.
The researchers report that 82 per cent of the participants regularly used MSG in food preparation, and the average intake was 0.33 g/day. Non-MSG users had an average BMI of 22.3 kg per sq. m, while MSG users had an average BMI 23.5 kg per sq. m.
Comparing people with the highest average MSG intake to those with the lowest, the researchers calculated that MSG users were likely to be overweight than non-users.
Indeed, high MSG consumption was associated with a 110 per cent increase in the risk of having a BMI of 23 kg per sq. m - considered overweight for Asian populations. Furthermore, high MSG consumption was linked to a 175 per cent increase in the risk of having a BMI of 25.0 kg per sq. m – the international standard for overweight.
“We found that prevalence of overweight was significantly higher in MSG users than in non-users,” He said. “We saw this risk even when we controlled for physical activity, total calorie intake and other possible explanations for the difference in body mass. The positive associations between MSG intake and overweight were consistent with data from animal studies.”
The researchers were affiliated with Fu Wai Hospital and Cardiovascular Institute at the Chinese Academy of Medical Sciences in Beijing, Northwestern University in Chicago and the INTERMAP Cooperative Research Group.
The Glutamate Association has led the challenge to the study. The association stated that the North Caroline study failed to account for other dietary sources of glutamate beyond soy sauce.
The association also noted that the average American consumes about one-tenth of a tea spoon of MSG per day, while total dietary consumption of glutamate is about 11 grams per day.
“In the He et al. study, the average BMI among non-MSG users versus the highest quartile of estimated MSG use was 22.3 versus 23.5. Given this small difference, the imprecise methods by which MSG intake was estimated, and controlled human studies that directly conflict with the results of this report, The Glutamate Association statement strongly questions the broad extrapolation made by the authors,” stated the association.
“Numerous regulatory authorities and expert bodies, including FAO/WHO, FDA, Health Canada, EFSA and FSANZ, all have concluded that MSG is safe for use as an ingredient in foods,” added the association.
Volume 16, Number 8, Pages 1875-1880. doi: 10.1038/oby.2008.274
"Association of Monosodium Glutamate Intake With Overweight in Chinese Adults: The INTERMAP Study"
Authors: K. He, L. Zhao, M.L. Daviglus, A.R. Dyer, L. Van Horn, D. Garside, L. Zhu, D. Guo, Y. Wu, B. Zhou, J. Stamler for the INTERMAP Cooperative Research Group