A staggering 52% of adults are overweight or obese across the EU on average, with more than half of adults in 18 of the 28 Member States affected, according to the latest figures available from the Organisation for Economic Co-operation and Development. Obesity rates vary widely, from a low of 8% in Romania and Switzerland to over 25% in Hungary and the UK, resulting in an overall average rate of 17%, or nearly one in five adults.
Most people recognise that being overweight is bad for them and there is a veritable frenzy of research into why those affected fail to manage their weight within healthy limits. Satiety offers a promising approach that could help people to feel fuller for longer (discouraging them from eating too often) and/or help them feel fuller sooner once they start eating (discouraging them from overeating during a meal).
One of the early ideas was to try to tap into a feedback mechanism called the ileal brake, where the arrival of nutrients at the bottom of the small intestine triggers the release of a cascade of satiety hormones that make us feel full. This literally puts the brakes on the digestion process, delaying gastric emptying and gastrointestinal transit. “The ileal brake is a highly satiating mechanism that results from fatty acids being absorbed at the end of the small intestine,” says Dr Alan Mackie from the Institute of Food Research (IFR). “It’s believed to be one reason why gastric bypass surgery is so successful in helping people lose weight.”
Not surprisingly, this attracted a lot of research interest for a while, with Unilever among the high-profile organisations exploring the ileal brake’s potential. However, it has proved extremely difficult to find a practical way to deliver an extra ‘hit’ of fats specifically to the right part of the gut when eating in a normal way. The result is that the focus of more recent effort has shifted up through the gut towards the top of the intestine, according to Mackie: “A lot of people are now turning to the effects in the upper small intestine.”
Digestive ‘brake’ (Return to top)
For example, he has been working together with research partners from the Dutch organisation Nizo to structure food so that the high-calorie, fatty components form a sediment at the bottom of the stomach, rather than floating on top of the stomach contents, as is more often the case. The researchers wanted to know whether they could use this to activate another feedback mechanism or digestive ‘brake’ by ensuring that the energy-dense portion of the meal hits the upper intestine first, rather than towards the end of the meal.
“In the small intestine, sensing cells detect fatty acids, amino acids and glucose and release gastro-intestinal hormones to slow down the emptying of the stomach,” says Mackie. The team reasoned that people should feel fuller for longer as a result.
The study combined magnetic resonance imaging (MRI) and blood tests to look at how two test meals were digested. Both meals contained similar nutrient compositions, with 67% of calories from fat, 27% from protein and 6% from carbohydrate. The test meal included a mixture of finely grated cheese and yogurt, which forms a semi-solid bolus that drops to the bottom of the stomach and forms a sediment.
“The protein drags the fat down,” says Mackie. “In the control meal we can see a layer of higher-fat materials at the top of the stomach. In the active meal the MRI scan shows dark regions towards the bottom of the stomach which are low in water. We just need some of that material to empty to provide the hit we're looking for.”
The team found that the main difference in stomach emptying rates occurred up to around 50 minutes after ingestion, when the emptying rate of the control meal was more than twice that for the active meal.
Regulating digestion (Return to top)
Investigators are also looking at other structural properties of foods that may play a role in regulating digestion and satiety. For example, research at the University of Birmingham recently caused a media flutter by coming up with an ingredients system that turns into a gel when it's exposed to stomach acid. The gel breaks down slowly, leaving the person feeling fuller for longer.
Similarly, some dietary fibres seem to offer a promising approach. Dupont Danisco recently enjoyed some experimental success with its Litesse Ultra polydextrose, for instance. Participants drank chocolate milk drinks containing varying doses of polydextrose and ate an unlimited, pasta-based meal 90 minutes later. The researchers found that the participants who consumed a higher dose of polydextrose ate fewer calories overall.
Meanwhile, Carmit Candy Industries has unveiled a weight-management chocolate bar that includes the powerfully water-binding soluble fibre glucomannan and Slendesta potato-derived proteinase inhibitor (PI2) from Kemin Industries. While glucomannan effectively adds calorie-free bulk, PI2 increases levels of cholecystokinin (CCK), which tells the brain that food has been eaten.
Satiety and the brain (Return to top)
And therein lies a big clue into how the approach to satiety has been evolving. Ultimately, satiety depends on the brain and, while relatively inert bulking agents such as hydrocolloid gels can fill the stomach, they have a limited impact on the complex interaction between gut cells and satiety hormones such as CCK, ghrelin, PYY or leptin.
“You’ve got all these feedback mechanisms that have evolved over millions of years to control how we eat,” says Mackie. “The body is incredibly good at controlling digestion, so trying to fool it is fiendishly difficult. You can get a feeling of being bloated rather than full unless you’re delivering at least some nutrients.”
What’s more, our mental attitude to food may have an even more powerful effect on the digestive process than previously realised. According to research reported at a meeting at Leatherhead Food Research (LFR) last year, Rick Mattes, a professor in the Department of Nutrition Science and director of the Ingestive Behavior Research Center at Purdue University reported that people had a completely different physical response when they believed that food became a solid in the gut, rather than becoming a liquid. This was despite the fact that trial participants were actually consuming the same juice-based products (solid and liquid), which either became or remained a liquid in their stomachs.
No magic bullet (Return to top)
“The physiological response matched people’s expectations,” says LFR nutrition research manager Dr Roberta Re. “Our perception of food has a big effect and we can use that to manipulate the physical response. So we’ve found that if you have a chocolate mousse and can maintain the mouthfeel of a high-calorie product, you can maintain a similar level of satiety in a lower-calorie version.”
However, Re also cautions that satiety is not a magic bullet to fix Europe's increasingly dysfunctional eating habits: “Eating behaviour is not just about physiology. If something looks good, we eat it. If someone else is eating, we eat it. If it’s the time we usually eat, we eat it. How many times do we eat when we’re not hungry or carry on when we’re full? And even if we purchase a product that's ‘cheating’ by being lower in calories, many of us will simply compensate and let ourselves eat more.”
She highlights an experiment carried out using identical cookies. When participants thought they were wholegrain, high-fibre and good for them, they ate significantly more than when they were told the cookies were a standard recipe.