Can a shake stop you snacking?

Mixing a common food additive into processed foods could “stave off hunger pangs for twice as long”, reported The Daily Telegraph. The newspaper said that “millions of dieters have been offered hope” by the process, which could mean the creation of cakes and pastries that stave off hunger pangs for longer.

The research by the Institute of Food Research looked at emulsifiers and stabilisers, which are extremely common in a range of processed food, from bread to salad dressings. These substances stop fat and water from separating in foodstuffs, and different additives may or may not break down in the stomach. The researchers chose a stabiliser called Tween 60, which does not break down in the acid of the stomach, and mixed it into a milkshake. After one hour, MRI scans showed that the volume of milkshake in the stomachs of those who had drunk the mixture was twice as great as in the stomachs of those who had drunk a similar shake without Tween 60. The subjects who drank the shake with the additive also said they felt fuller and less hungry.

This was preliminary research in 11 men in their twenties and is insufficient to offer hope to dieters. Regardless of whether people who feel full eat fewer calories in the long term, the study does not promote the addition of this substance to fast foods, as implied by some newspapers. These energy-dense foods have high levels of saturated fat and sugar, and this study should not be taken as an excuse to eat unhealthily. 

Where did the story come from?

This research was conducted by Dr Luca Marciani and colleagues from the Wolfson Digestive Diseases Centre and other departments in the University of Nottingham. The study was funded by the Biotechnology and Biological Sciences Research Council and published in the peer-reviewed British Journal of Nutrition.

What kind of scientific study was this?

This was a controlled trial comparing the stability of two fat/water emulsion meals in the gastric environment. The researchers explained that fat is often included in common foods as an emulsion of dispersed oil droplets to enhance the look, smell and texture of the food and to improve its stability.

The researchers had a theory that the stability of emulsified fat in the acidic environment of the stomach may affect how fast the stomach emptied, the sensation of fullness (satiety) and the absorption of fats.

They compared an acid-unstable emulsion with an acid-stable fat emulsion to see if the acid-stable one would empty from the stomach more slowly, cause more rapid lipid absorption and lead to a greater feeling of fullness.

Twelve healthy male volunteers were recruited and assessed for general health using a questionnaire. They had an average age of 24 and a BMI of 23.8kg/m2. The volunteers were checked to see if they had any reasons why they could not have an MRI scan and were given blood tests to check for lipids, anaemia and glucose. One volunteer withdrew from the study as he did not want to have blood tests taken.

The remainder were invited to two separate morning experiment sessions (about a week apart), having fasted overnight on each occasion.

Two test meals were developed for the study, with equal fat content (50g fat), equal energy content (3150kJ) and equal mean oil droplet size distribution (3.6mm). The acid-stable emulsion meal was designed to remain intact in the acid gastric environment and the other was designed to break down in two distinct phases.

At each session, the volunteers drank a 500ml serving of one of the two emulsion meals. The order in which they were given the drink was allocated at random. After 4.5 hours they ate a standard, low-fat cheese and salad sandwich with still water. This meal was chosen because it was low in fat.

The volunteers’ sense of fullness, appetite and hunger was monitored when they were given the drink and at hourly intervals for 12 hours using a 10-point visual scale. The volume of the meal was assessed over time using MRI scans, manually tracing the region of interest using special software. Scans were taken approximately every 20 minutes for about four hours.

What were the results of the study?

The researchers say that the acid-unstable fat emulsion broke up and formed layers in the stomach quickly, while the gastric emptying of meal volume was slower for the acid-stable fat emulsion. The rate of energy delivery of fat from the stomach to the duodenum (part of the small intestine) was no different for both emulsions for up to 110 minutes.

Judged using the visual scales, the acid-stable emulsion induced increased fullness, decreased hunger and decreased appetite. All these changes were statistically significant.

What interpretations did the researchers draw from these results?

The researchers said that this study shows “it is possible to delay gastric emptying and increase satiety by stabilising the distribution of fat emulsions [within the stomach] against the gastric acid environment.” They claim that this could have implications for the design of novel foods.

What does the NHS Knowledge Service make of this study?

This small study in human volunteers has further tested the properties of an acid-stable emulsion and confirmed that it remains stable in human experimental conditions. There are some limitations to the study worth noting:

• The researchers and volunteers were not blinded to the identities of the experimental drinks and so it is possible that they knew which drink they were being given. This may have affected the interpretation of results by the researchers and could have influenced how the volunteers filled in the visual scales. Ideally, the identities of the drinks should have been concealed from both groups of people.
• The research measured the participants’ hunger, satiety and appetite using a visual scale, but these are subjective measures. Also, the differences in scores were not statistically different at all time points, often with less than two points’ difference on the 10-point scale. When combined with the lack of blinding, it is not possible to say how important or valid this difference was.
• It is not clear how the researchers validated the measurement of meal volume using the MRI scans against actual stomach size.
• The link between satiety and weight loss needs further testing. For example, it is possible that feeling fuller immediately after a meal is not linked with reduced energy intake and weight loss over the long term.

Overall, this study confirms the expected action of an acid-stable emulsifier on separation within the stomach.

While it has been suggested that this will have benefits in reducing appetite in other foods or in real-life situations, this will need testing in further research, preferably using blinded, randomised studies.

Newspaper articles have reported that this emulsion could be added to fast foods and have highlighted the possibilities of being able to eat burgers, hotdogs, chips and pastries and feel full for longer. Regardless of whether this is a possibility, the study does not promote the addition of this substance to such foods.

These energy-dense foods have high levels of saturated fat and sugar and this study should not be taken as an excuse to eat an unhealthy diet.