Why do we fill up on a small bowl of porridge, yet happily chomp through an entire packet of Tim Tams and still have room for more? Dietitian Brooke Longfield shares the key to lasting satiety.
Feeling full is an important part of being satisfied with what we eat. As anyone who’s been on a diet knows, when we miss out on that feeling of fullness at the end of a meal, it can trigger cravings. Unfortunately, cravings can lead to unhealthy snacking as we search for that satisfying sensation of fullness in our tummies.
Can this feeling be triggered without overeating? The good news is, yes! Researchers have learned that key elements within foods encourage fullness. And, a satiating diet is a strategy many nutrition experts use to combat the obsesity crisis. As Professor Jennie Brand-Miller, PhD, explains, “There appears to be a hierarchy of nutrients, and some satisfy more than others. Protein is the most satiating, followed by carbs, then by fat. Increasing evidence shows that high-fibre foods and low glycaemic-index foods also fill you up.” So believe it or not, we want you to eat more — just of the right foods. Let’s look at how to add these nutrients into our meals and make them work for you!
The power of protein
Protein has incredible power over our appetites. Studies show the most effective way to stimulate the release of the satiety hormones which tell the brain that you’re full, is to eat protein-rich foods such as meat, fish, eggs and legumes (such as beans, chickpeas and lentils).
The emerging scientific view is a theory of ‘protein leverage’, meaning the body needs to reach a fixed protein target for optimal function. In other words, we are programmed to keep eating until we get enough of this nutrient. According to this theory, hunger only goes once we’ve hit our individual protein targets, and those who follow low-protein diets risk overeating.
In 2011, Aussie researchers had an interesting finding when they put one group of people on a diet of 10 per cent protein, and the other group on a diet with 15 per cent protein. People on a low-protein diet consumed 12 per cent more kilojoules than those on the high-protein diet. Those who also ate more protein were less hungry and less likely to snack.
One of the most important and renowned dietary studies of the past decade is the DiOGenes (Diet, Obesity and Genes) project. It aims to pinpoint the best diet for the prevention of obesity.
In 2010, the DiOGenes project focused on people who had lost weight to learn what diet would help them maintain their weight loss. Interestingly, people who ate a low glycaemic-index (low-GI) diet that was high in protein were more likely to maintain their new weight compared with those on
a low-protein, high-GI diet.
Better still, the group who ate a diet high in protein went on to lose more weight without really trying, and 12 months later, had managed to keep it off.
Researchers credit the success of the diet to feeling full without counting kilojoules.
The group who followed a high-protein, low-GI diet also had the lowest drop-out rate, indicating that people found the diet sustainable.
You only have to compare bran twigs with rice bubbles to see that high-fibre foods are great for scrapping hunger. The airy bubbles will send you searching for a second brekkie within the hour, whereas the fibrous twigs should see you through to lunch. The rough stuff satisfies with its texture, its structure and its action in the body.
High-fibre foods such as fruit, vegies, nuts and whole grains, need plenty of chewing. All this activity gets our saliva and gastric juices going, causing the stomach to expand and promoting satiety. This explains why a whole apple is more filling than apple juice, even though you’re drinking the juice of four to five apples.
Leafy and fibrous foods such as spinach, celery and corn, are full of insoluble fibre, providing satisfying bulk for few kilojoules.
So it was no real surprise that a 2001 US study found people who increased their daily fibre by 14g ended up eating less food and 10 per cent fewer kilojoules. It’s yet another good reason to pile our plates with fresh vegies that are stacked with fibre.
Soluble fibre and protein create the feeling of fullness in different ways. Fibre slows digestion, and helps to stabilise blood-sugar levels between meals, staving off that hangry (hungry and angry) feeling! Good sources of soluble fibre include rolled oats, legumes, beans, psyllium husks, apples and blueberries. So tuck in!
Clever low-GI carbs
Carbohydrates have long been a subject of debate among people watching their weight. But it pays to remember not all carbohydrates are created equal. After all, lentils and lollipops are both forms of carbohydrate, but sugary sweets are no match for healthy legumes! We need to consider the quality of the carbs and their effect on the body. This is where glycaemic index (GI) comes into play.
The body works hard to break down low-GI carbs such as wholegrain bread, baked beans and apples. As a result, blood-sugar levels rise steadily, providing sustained energy and keeping hunger at bay.
In contrast, high-GI carbohydrates such as white bread, biscuits and white rice are much easier to digest. Their rapid assimilation causes blood-sugar levels to spike and then quickly drop. (Think of the energy slump you often experience half an hour after having a sugary drink or chocolate bar.)
In a 2003 UK study of schoolchildren, the GI score of their breakfast had a knock-on effect. Students who had a low-GI breakfast ate less at lunch. They also rated themselves as less hungry before lunch compared with those who ate a high-GI brekkie.
Other studies reveal people want more food after eating a high-GI meal than they do after eating low-GI foods.
This supports the current view that eating low-GI foods prolongs satiety and helps curb hunger.
There’s no denying fat means flavour. In fact, our taste buds are designed to love the feel of high-fat foods such as choccies, ice cream and cheesecake. The urge to eat kilojoule-rich fat is what kept our primitive ancestors alive when food was scarce.
Despite this, studies show (somewhat counterintuitively!) that fat is less satisfying than protein and carbohydrates.
In a UK study, obese people who were given high-fat foods consumed twice the amount of kilojoules than when they ate high-carbohydrate varieties.
Also, women who snacked on high-protein yoghurt for a 2014 US study had stronger feelings of fullness than those who ate fatty crackers or chocolate.
So if fat isn’t all that satisfying, why do we feel ‘stuffed’ after indulging in rich, high-fat food?
Take Christmas, for instance — we’ve had a huge meal and feel full, perhaps uncomfortably so, yet we still pick at rich pudding, shortbread and chocolate. Why? Because fat overrides our bodies’ normal appetite signals.
In 2005, Swedish researchers found palatable fatty and sugary foods disrupt our natural appetite regulation. This ramps up our hunger signals and drives us to eat more to reward our brain’s pleasure centres.
Gram for gram, fat has twice the kilojoules of protein and carbs. So if you rely on chips, biscuits or cheese to satisfy your hunger, you’ll be taking in hundreds of extra kilojoules – far more than if you’d reached for foods high in protein or fibre.
Feel full on fewer kilojoules
Most of us eat the same volume of food every day. Choosing foods with a high volume for few kilojoules can help us to feel full without gaining weight.
Compare a cup of carrot sticks with a cup of potato chips, for example. The crudités weigh more, yet only have a tenth of the kilojoules of the chips. This means the carrots have a low ‘energy density’. Dietitians use this term to describe how much energy (kilojoules or calories) a food provides per gram.
Foods that contain plenty of water add bulk to meals with zero kilojoules. Fruit and vegies are prime examples, particularly watermelon, berries, zucchini, spinach and carrots. These low energy-dense foods tend to also be high in fibre and low in fat. Other examples are whole grains, pasta and rice, which you cook in water. This lowers their energy density even more. Low-energy density foods provide fewer kilojoules per gram than high-energy density foods. So you can enjoy more food without overeating kilojoules.
At the other end of the spectrum, foods with a high-energy density, pack a big kilojoule punch in a small package. Usually high in fat and low in water, they include biscuits, chocolate, cheese and fried foods. Overeating high energy-dense foods easily leads to weight gain.
If you’re trying to lose weight and don’t want to feel deprived, choose high-fibre foods with a high water content. You’ll literally fill your stomach with food without eating a truckload of extra kilojoules.
The anatomy of appetite
Our appetites keep us alive. Food is fuel, and our body’s innate sense of hunger drives us to eat so we both survive and thrive. But what drives hunger? The mechanism is complex, but hormones are a key piece of the puzzle.
The brain and gut work together to regulate appetite. From the moment we start eating, the gut sends hunger and satiety hormones to the brain, the control centre that interprets these messages and determines whether or not we need to eat.
Keep in mind, the brain can take 15 to 20 minutes to fully register these signals. So if you eat too quickly you can override these signals and overeat.
The two main hormones at work here are hunger-stimulating ghrelin and appetite-suppressing leptin. An empty stomach releases ghrelin, which sends the message ‘feed me’ to the brain, stimulating appetite.
Leptin has the opposite role. When we’re full, our fat cells will trigger leptin which reduces appetite. It tells the brain we’ve had enough and it’s time to burn kilojoules. Essentially, the more body fat you have, the more leptin you produce. This means you should quickly realise you’ve had enough to eat, but overweight people’s chronically high leptin levels desensitise their brains to this hormone, making them more likely to overeat.
Factor fullness into your day
A successful eating plan will provide food that leaves you feeling full, slaying the temptation to snack on anything (and everything) between meals. Surprisingly, some of the most palate-pleasing foods such as fat-rich chocolate and greasy chips, fail to deliver such satisfaction. To improve your satiety, increase your intake of protein, fibre and low-GI carbs. These appear to work best in combination.
Of course, when we shop and cook, we focus on real ingredients and food, not individual nutrients. See our super-satisfying seven-day meal plan PDF (see Downloads, below) that includes nutritionally balanced meals and snacks to keep you feeling full and satisfied on fewer kilojoules, but not necessarily less food!
What really satisfies?
If you’re wondering which foods are the most filling, we’ve found the answers. Scientists at The University of Sydney developed a handy ‘satiety index’ of 38 common foods. Using white bread as a baseline (at 100), this scale ranks foods in order of their ability to satisfy hunger, and the results will surprise you. Some foods, such as croissants and cakes, are half as satisfying as white bread, whereas boiled potatoes are three times more satisfying.
The Satiety Index
See how everyday foods stack up, from the most satisfying to the least.
Three times more satisfying than white bread
Satisfies for just a few kJs!
Often overlooked, they add satisfaction
Breakfast bran twigs
Half as satisfying as white bread
Five feel-full tips
Replace low-fibre Turkish bread, white crumpets and white toast with authentic low-GI sourdough or high-fibre dense, grainy breads such as soy–linseed.
Make your usual bolognese or chilli con carne even more satisfying by adding protein-rich lentils or red kidney beans to the lean-mince mix.
Sip a milk-based fruit smoothie as a satisfying grab-and-go breakfast.
Give homemade cakes, muffins and biscuits a low-GI makeover by swapping white flour for unprocessed oat bran or chickpea flour.
Store crunchy low-kilojoule carrot and celery sticks in clear containers at the front of the fridge. Snack on these crudités (rather than chocolate and biscuits) when hunger or boredom strikes.
Are you really hungry?
Most of us know all too well that there’s more to hunger than a growling stomach.
Our emotions can have an enormous impact on our appetite — sadness, anger or simple boredom can drive us to eat … and eat … and eat. Before you take a bite, think about the type of hunger you’re feeling.
The word hunger is defined as “a feeling of discomfort or weakness caused by lack of food”. Sadly, thanks to the constant presence of food and drink, few of us experience true hunger.
You’ve just eaten, but the sight and smell of a freshly-baked batch of brownies is enough to make your mouth water, even though you’re full.
Has it hit midday and your first thought is ‘lunchtime’? Eat in response to your body’s natural hunger cues, not the clock.
Many of us will eat to fill an emotional void when we feel like we’re missing something. Be mindful of using food as a crutch for your feelings. Try to distinguish this behaviour from true hunger.
Dehydration can leave you feeling fatigued, which you can easily mistake for hunger. If you’re peckish, see if a glass of water satisfies.