THE steaming plate of fish balls in tomato sauce looks and smells appetising enough, but I hesitate to tuck in, and not just because it's 10 in the morning. These processed balls are no ordinary food: they could represent the future of the weight loss industry.
Think of diet food and what usually springs to mind is tiny portions of insubstantial fare. Not so for a range of foods designed to work by being more filling than usual – meaning that, in theory, you should eat less.
The super-satiating foods being put through their paces at the University of Liverpool in the UK – where I am today – and other places around Europe have been made possible because of our growing understanding of how our bodies control appetite. It's not just the signalling between our brain and our belly that we are getting to grips with, but also the influence of the microbes that make our gut their home.
The pay-off could be a range of ways to make it easier for people to control their weight. Not only could we choose existing foods more wisely, but soon we may be eating a range of super-filling products – apart from fish balls, other things on the menu include bread, yogurt, smoothies, soups and sauces.
If the trials go well, such products could be on the shelves in the next few years. But is the plate of food in front of me really the future for healthy eating – or does it miss the point?
Our feelings of fullness are governed by a complex mix of factors, including the physical feeling of our stomach stretching, and the chemical and hormonal signals the food triggers arriving in our brains.
Foods high in protein and fibre are particularly good at this (see "Weighty questions"). Some food manufacturers have already started marketing diet foods that are supposed to keep people fuller for longer, based on these principles.
But there may be ways to push our satiety buttons harder still, thanks to the growing realisation that certain types of carbohydrate are particularly good at sending fullness signals from the gut to the brain.
The compounds are a type of starch, naturally present in certain plants, which cannot be broken down by the enzymes in our small intestine, where most of our food is absorbed. Only when this "resistant starch" reaches our lower bowel is it finally digested by the resident bacteria, which release chemicals called short-chain fatty acids.
These chemicals send messages to the brain that starch is reaching the lower gut without being digested. "That tells the brain to slow up on the input," says Stephen Bloom of Imperial College London, who helped discover some of these mechanisms.
Resistant starches occur naturally in peas, beans and lentils, as well as forming in starchy foods like potatoes, pasta and rice if they are cooked then allowed to cool down.
So could we create a wider range of foods that help people lose weight by adding resistant starch or other satiety-enhancing ingredients? That is the aim of the SATIN project – a consortium of seven European universities and 11 food companies.
With our gut microbes having such an important role in the break down of resistant starch, a crucial player has been a Belgian lab that aims to recreate the gut's complex ecosystems.
Five microbial soups stand in for the main chambers of the human digestive system: the stomach, small intestine and the three parts of the lower bowel. Mechanically chewed up meals are fed into the stomach, then tubes take the slurry to each flask in turn – the contents getting progressively browner. "It's like having a person laying on a bench," says Massimo Marzorati, of ProDigest, the firm that runs the system.
The set-up allows Marzorati's team to check that when resistant starches are mixed into new foods, they still do their job. They have tested about 50 products so far. Several have made it into human trials to see whether they help people control their weight – and, crucially, whether the grub is any good.
This is where the fish balls in front of me, which contain resistant starch made from carob beans, started out. Their texture seems fine and they are tasty enough, although I can't face a whole plateful as a mid-morning snack. Good thing, too, as resistant starch can have some unpleasant side effects. Feeding our gut bacteria means they release carbon dioxide, and the short-chain fatty acids can irritate the bowel. The end result? Farting and diarrhoea.
Fortunately, I suffer no such collateral damage – and Jason Halford, who helps run the Liverpool research, says those effects haven't been showing up in their trials so far.
Of course, the proof of the pudding is whether the super-satiating foods actually help people shed the pounds. Halford is reluctant to tell me how the trials have been going on that front until the results are published. What he will say is that preliminary results from a small placebo-controlled trial of people eating modified tomato soup every day suggests that it does reduce the amount of other foods someone eats.
I can't help wondering, though, if it's worth spending all this money – €6 million so far – on developing yet more highly processed foods – meals that will be more expensive to buy than their fresh plant-based ingredients. "Eating natural foods is cheaper and more effective," says Bloom, who isn't part of the SATIN consortium.
"The problem is that, by and large, people aren't consuming them," counters Halford. However, he admits that the foods in development won't be a panacea to the Western world's obesity problem. "But if we can develop processed foods that are healthy and benefit appetite control we can make a positive impact on people's lives," he says.
Certainly, we haven't had much luck at convincing people to turn their backs on the typical Western diet of white bread and junk food. Most dieters end up putting the weight back on, and more.
Gary Frost of Imperial College London thinks super-satiating foods are more likely to help people maintain a steady weight, rather than lose it. He is developing breads and smoothies based on a similar premise to Halford's, only they are fortified with the short-chain fatty acids that are the gut bacteria's output. Initial trials in people suggest foods containing it help reduce weight regain after dieting.
Una Masic, who is involved in the Liverpool trials, thinks resistant starch shouldn't be used as a quick fix. "A diet should be for life, not just a month," she says.
Even if people don't want to buy modified meals, just knowing which natural foods are the most filling should help people design their own meals better. This is where a new satiation index comes in. "There are 30,000 foods out there, and there are big databases on them but they don't tell you anything about how filling those foods are," says James Stubbs of the University of Derby in the UK.
Stubbs is working with UK weight loss firm Slimming World to develop a satiety quotient for many foods, based on studies that have measured how much people eat at a subsequent meal. He thinks that just as dieters check a food's calories, in future they will also consider its satiety quotient. "If you can navigate towards foods that are filling then you can manage your weight better," he says.
This article appeared in print under the headline "Winning at the hunger games"
Clare Wilson, Winning at the hunger games. New Scientist, 2015; Issue 3026,14-15.