Wednesday July 23 2014
Umami is a Japanese term that describes a savoury taste
"Always hungry? You need more umami in your life: study finds so-called 'fifth taste' in sauces and meat helps us feel satisfied," reports the Mail Online.
Umami is a Japanese term that roughly translates as "pleasant savoury taste" and has been described as the fifth taste, the other four being sweet, sour, bitter and salty.
The sensation of eating umami-rich food, such as soy sauce and shellfish, is caused by glutamate. Glutamate is an amino acid, a building block of proteins. The salt form, monosodium glutamate (MSG), is a flavour enhancer.
In this study, researchers proposed that another chemical, inosine-5'-monophosphate (IMP), which is also derived from an amino acid, may act synergistically with MSG to improve flavour and increase feelings of fullness.
To test the effect of MSG and IMP, researchers gave 27 participants one of four types of carrot soup 45 minutes before giving them lunch.
Participants were either given a plain carrot soup, carrot soup with added MSG and IMP, carrot soup with added protein and carbohydrate, or carrot soup with added protein, carbohydrate, MSG and IMP.
The researchers then looked at how the soups influenced how much food the participants ate at lunch, as well as how the soups affected the participants' mood and appetite.
They found adding MSG and IMP caused an immediate increase in appetite, but people then ate less at lunch. It is possible eating a healthy umami-rich breakfast, such as tomatoes and mushrooms, could reduce cravings later in the day.
Where did the story come from?
The study was carried out by researchers from the University of Sussex and was funded by Ajinomoto North America, Inc.
Ajinomoto is a Japanese food and chemical corporation that produces a number of products, including the chemicals used in this study: monosodium glutamate (MSG) and inosine-5'-monophoshate (IMP).
In fact, the founder of the company discovered the "umami" taste and invented MSG as a seasoning that captures this taste.
The researchers state Ajinomoto had no role in the study design, data collection or analysis.
The study was published in the peer-reviewed American Journal of Clinical Nutrition.
The research was reported in the Mail Online, who seemed to have got most of their coverage from another website, Medical Daily.
Although the conclusions from the study are basically correct, many of the details of how the study was performed are wrong.
For example, the Mail says only two types of soup were used by the researchers, when in fact four types were used.
What kind of research was this?
This was a crossover trial. In this trial, each participant ate one of four different soups on four non-consecutive days to see if the addition of the following substances influenced how much pasta they ate 45 minutes later:
- protein and carbohydrate
- MSG and IMP
- protein, carbohydrate, MSG and IMP
What did the research involve?
The researchers recruited 27 people into the study. Participants were studied on four non-consecutive days and told to fast from 11pm the night prior to one of the study days.
On the study day, they were given breakfast (a fixed portion of milk and cereal with juice) and told to only drink water until they returned three hours later.
When they returned, they were asked to rate how alert, clear-headed, energetic, full, hungry, nauseous and thirsty they felt.
They were then given a sample of spiced carrot soup. The soup was either:
- spiced carrot soup (low-energy control)
- spiced carrot soup with added maltodextrin (a carbohydrate) and whey protein (high-energy, high-carbohydrate, high-protein soup)
- spiced carrot soup with MSG and IMP (low-energy soup plus MSG and IMP)
- spiced carrot soup with added maltodextrin and whey protein plus MSG and IMP (high-energy, high-carbohydrate, high-protein soup plus MSG and IMP)
Participants were asked to rate how filling, pleasant, salty, savoury, strong and sweet the sample was, and also rated their appetite.
They were then given a 450g bowl of soup and were asked to rate their appetite every time they ate 50g.
Forty-five minutes later, the participants were again asked to rate how alert, clear-headed, energetic, full, hungry, nauseous and thirsty they felt.
They were then provided with lunch, which was a 450g plate of pasta with sauce, and instructed to eat as much as they liked until they felt comfortably full. A refill was provided when only 50g of pasta remained.
Appetite and mood ratings were assessed again after lunch. The researchers looked at how the different soups influenced how much pasta was eaten at lunch and participants' ratings of appetite and mood.
What were the basic results?
The researchers found:
- people ate less pasta at lunch if MSG and IMP were added to the soups
- people ate less pasta at lunch if they had previously been given the high-energy, high-carbohydrate, high-protein soup
The researchers looked at whether the addition of MSG and IMP to the high-energy, high-carbohydrate, high-protein soup influenced the amount of pasta people ate.
They found people were able to compensate better for the calories they had eaten in the soup by eating less pasta after eating the soup with MSG and IMP.
The researchers also found the addition of MSG and IMP to soup increased ratings of the soup's pleasantness and caused an immediate increase in appetite when the soup was first tasted. However, this increase in hunger was not maintained.
How did the researchers interpret the results?
The researchers concluded this study has shown MSG and IMP had two effects on appetite:
- it acts to stimulate hunger when it is first tasted as a result of increased palatability
- it then acts to enhance feelings of being full
In this study, researchers have found adding MSG and IMP to soup increased the soup's pleasantness and caused an immediate increase in appetite when it was first tasted, but people ate less food 45 minutes later if they had been given a soup containing MSG and IMP.
This study involved a small number of participants, which limits the reliability of any of the results. It may be the case similar results would have been obtained had hundreds of people been studied, but this cannot be assumed. Similarly, the study only tested a specific scenario of eating enhanced soup followed by pasta.
It remains to be determined whether adding these chemicals to food on a long-term basis would result in any health benefits or, most importantly, any harms.
It should also not be assumed from this study that, if the combination of MSG and IMP acts to enhance satiety, these chemicals should necessarily be used in the battle against obesity – for example, by adding them to soups or drinks to stop people snacking or eating more at mealtimes.
The best way of staying healthy is to eat a balanced diet high in fruit and vegetables and low in saturated fats, salt and sugars.
The eatwell plate highlights the different types of food that make up our diet, and shows the proportions we should eat them in to have a well-balanced and healthy diet.
It is also important to take regular exercise in line with recommendations.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.