Researchers from Ajinomoto report in the journal Physiology & Behavior that rats given free access to water containing the flavor enhancer gained less weight, and deposited less fat, without affecting blood pressure, lean body mass or food and energy intake.
The study results come in stark contrast to recent findings from the University of North Carolina (UNC) that linked MSG consumption in humans to weight gain.
UNC lead researcher Ka He, MD, claimed at the time of the publication that the findings were the first to find a link between MSG use and weight in humans after previous animal studies had suggested similar results.
The Ajinomoto researchers fed Sprague-Dawley rats diets with varying calorific density, fat and carbohydrate levels, and giving them free access to an MSG-containing solution. The researchers report that between 93 to 97 percent of the animals showed a preference for the MSG solution, over just water alone.
The animals that ingested MSG were reported to have significantly less weight gain, and reduced abdominal fat mass, compared to rats ingesting only water. Moreover, lower plasma leptin levels were observed.
“These changes are likely to be mediated by increased energy expenditure, not reduced energy intake or delayed development,” said the researchers.
None of the other variables measured, including lean mass, food and energy intakes, blood pressure, glucose or insulin levels, or GLU were affected, said the researchers. MSG is the sodium salt of the amino acid L-glutamate (GLU).
“The present study provides the first evidence that young rats allowed spontaneously to consume MSG exhibit reduced weight gain, fat deposition (fat mass), and plasma leptin levels, compared to rats consuming vehicle (water),” wrote the researchers. “Together, these results suggest that conceivably, MSG might prove useful in reducing fat deposition and obesity.”
In August, UNC researchers reported opposite effects of MSG ingestion in humans. 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.
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.
“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.”
Source: Physiology & BehaviorSeptember 2008, Volume 95, Issues 1-2, Pages 135-144 "MSG intake suppresses weight gain, fat deposition, and plasma leptin levels in male Sprague–Dawley rats"Authors: Takashi Kondoh, Kunio Torii