Why do we fill up on a small bowl of porridge, yet happily chomp through four or five chocolate bikkies and still have room for more? Dietitian Brooke Longfield shares the key to feeling satisfied for longer.
Feeling full is an important part of being satisfied with what we eat. As anyone who has 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 comforting 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 (satisfying) diet is a strategy many nutrition experts use to combat obesity. As Jennie Brand-Miller, Professor of Nutrition at the University of Sydney, 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.”
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 satiety hormones that tell the brain you’re full, is to include protein-rich foods such as meat, fish, eggs and legumes such as beans, chickpeas and lentils.
An emerging scientific view is the 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. This means hunger only goes once we’ve hit our individual protein targets, and those who eat low-protein diets risk overeating.
In 2011, Australian researchers came up with an interesting finding when they put one group of people on a diet with 10 per cent energy (kilojoules) from protein and another group on a diet with 15 per cent energy from protein. People on the lower-protein diet consumed 12 per cent more kilojoules than those on the higher-protein diet, and this group also reported feeling less hungry and less likely to snack.
In 2010, the DiOGenes (Diet, obesity and genes) 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 kept 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 dropout rate, indicating people found the diet sustainable.
Our menu plans in each issue of Healthy Food Guide average about 22 per cent energy from protein.
You only have to compare oats with rice bubbles to see that high-fibre foods are great for scrapping hunger. The light, airy bubbles will send you searching for a second brekkie within the hour, whereas the fibre in oats could 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, veges, nuts and whole grains need plenty of chewing. All this activity gets our saliva and gastric juices going, promoting satiety and causing the stomach to expand. This explains why a whole apple is more filling than apple juice, even though you can be drinking the juice of several apples.
Leafy and fibrous foods such as spinach and celery, as well as the skins of other veges and fruits, are full of insoluble fibre, adding 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 veges that are stacked with fibre.
Soluble fibre also creates the feeling of fullness; it 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, carrots, broccoli, Brussels sprouts, apples and berries. 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) can be helpful. 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 more slowly and 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.
In a 2003 UK study of school children, 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 meals prolongs satiety and helps to curb hunger.
Our taste buds are designed to love the feel of high-fat foods such as chocolate, ice cream and cheesecake. The urge to eat kilojoule-rich fat is what helped to keep 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 — you’ve had a huge meal and feel full, perhaps uncomfortably so, yet you still pick at rich pudding, shortbread and chocolate. Why? Because fat can override 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 the pleasure centres in our brain.
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 roughly the same volume of food every day. Choosing foods with a high volume but fewer 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 have less than a fifth of the kilojoules of the chips. This means the carrots have a low ‘energy density’. Dietitians and nutritionists use this term to describe how much energy (kilojoules) a food provides per gram.
Foods that contain plenty of water add bulk to meals with fewer kilojoules. Fruit and veges such as berries, courgettes, spinach and carrots are prime examples. These low energy-dense foods tend to also be high in fibre and low in fat.
Other examples are whole grains, pasta and rice that you cook in water, which lowers their energy density. Low-energy dense foods provide fewer kilojoules per gram than high-energy dense 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 leads to weight gain.
If you’re trying to lose weight and don’t want to feel deprived, choose high-fibre foods with 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 15-20 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 the appetite.
Leptin has the opposite role. When we’re full, our fat cells trigger leptin which tells the brain we’ve had enough and reduces appetite. 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 it appears many overweight people may have chronically high leptin levels that desensitise their brains to this hormone and its message, 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, aim to include protein foods at each meal, increase fibre intake and choose 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. Turn to page 60 for our seven-day menu plan that includes nutritionally balanced meals and snacks to keep you feeling full and satisfied on fewer kilojoules, but not less food!
Five feel-full tips
- Replace low-fibre French bread, white crumpets and white toast with high-fibre dense, grainy breads or authentic sourdough, which is low-GI.
- 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.
- 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.
- Snack on a handful of nuts, rather than muffins or biscuits.
Make the more satisfying choice the easier choice by making these foods staples in your home
- Canned legumes such as lentils, chickpeas, red kidney beans and cannellini beans: High in fibre these add protein too. Add to soups, salads and casseroles or have baked beans on toast.
- Trim milk: We often think of milk ‘just as a drink’, but it’s a protein-rich food. By itself or in a smoothie this is the basis of a satisfying breakfast or snack.
- Nuts: Put them into small snack-size bags. Thanks to their protein and fibre a small amount can really satisfy.
- Low-energy veges: Superstars in so many ways! Packed with nutrients and flavour, they add interest and texture to our meals and snacks while helping us feel full.
- Low-fat yoghurt: Add protein at snack time or add to cereals and smoothies.
- Berries: Keep these sweeties on-hand in the freezer to use at breakfast, in smoothies or as the base for a healthy dessert.
- Eggs: Ever noticed how filling eggs are for breakfast? A boiled egg makes a great snack too.
- All Bran and wholegrain rolled oats: These filling cereals add fibre and protein.
- Brown rice and wholegrain pasta and couscous: For more satisfying fibre than white variants.
- Barley, buckwheat and quinoa: These low-GI wholegrains will satisfy more than white rice or quick-cook noodles.
Are you really hungry?
Most of us know only 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.
- True hunger: The word hunger is defined as “a feeling of discomfort or weakness caused by lack of food”. Thanks to the constant presence of food and drink, few of us experience true hunger.
- Mouth hunger: You have 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.
- Mind hunger: Has it hit midday and your first thought is ‘lunchtime’? Eat in response to your body’s natural hunger cues, not the clock.
- Emotional hunger: 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.
- Thirst: Dehydration can leave you feeling fatigued, which you can easily mistake for hunger. If you’re peckish, see if a glass of water satisfies.
Article sources and references
- Blundell et al. 1993. Dietary fat and the control of energy intake: Evaluating the effects of fat on meal size and postmeal satiety. American Journal of Clinical Nutrition. 57:S772—7https://www.ncbi.nlm.nih.gov/pubmed/8475895
- Crujeiras et al. 2010. Weight regain after a diet-induced loss is predicted by higher baseline leptin and lower ghrelin plasma levels. Journal of Clinical Endocrinology & Metabolism 95:5037-44https://www.ncbi.nlm.nih.gov/pubmed/20719836
- Gosby et al. 2011. Testing protein leverage in lean humans: A randomised controlled experimental study. PLoS ONE 6: e25929https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0025929
- Howarth NC et al. 2001. Dietary fibre and weight regulation. Nutrition Reviews. 59: 129-139https://www.ncbi.nlm.nih.gov/pubmed/11396693
- Journel et al. 2012. Brain responses to high-protein diets. Advances in Nutrition 3:322-9https://academic.oup.com/advances/article/3/3/322/4591532
- Larsen et al. 2010. Diets with high or low protein content and glycemic index for weight-loss maintenance. New England Journal of Medicine 363:2102-13https://www.nejm.org/doi/full/10.1056/nejmoa1007137
- Martens et al. 2012. Protein leverage affects energy intake of high-protein diets in humans. American Journal of Clinical Nutrition 97:86-93https://academic.oup.com/ajcn/article/97/1/86/4577132
- Myers MG et al. 2010. Obesity and leptin resistance: Distinguishing cause from effect. Trends in Endocrinology Metabolism 21: 643-51https://www.ncbi.nlm.nih.gov/pubmed/20846876
- Obesity Action Coalition. 2015. Grehlin, the “Go” Hormone www. obesityaction.org Accessed July 2015https://www.obesityaction.org/
- Ortinau LC et al. 2014. Effects of high-protein vs high-fat snacks on appetite control, satiety, and eating initiation in healthy women. Nutrition Journal 13:97https://www.ncbi.nlm.nih.gov/pubmed/25266206
- Psych Central. 2015. What is real hunger? www.psychcentral.com Accessed July 2015https://psychcentral.com/
- Simpson et al. 2003. Geometric analysis of macronutrient intake in humans: The power of protein? Appetite 41:123-40https://www.ncbi.nlm.nih.gov/pubmed/14550310
- Slavin J & Green H. 2007. Dietary fibre and satiety. Nutrition Bulletin 32:32-42https://onlinelibrary.wiley.com/doi/full/10.1111/j.1467-3010.2007.00603.x
- Warren JM et al. 2003. Low glycemic index breakfasts and reduced food intake in preadolescent children. Pediatrics 112: e414-9https://www.ncbi.nlm.nih.gov/pubmed/14595085
- Weigle et al. 2005. A high-protein diet induces sustained reductions in appetite, ad libitum caloric intakes, and body weight despite compensatory changes in diurnal plasma leptin and ghrelin concentrations. American Journal of Clinical Nutrition 82: 41-48https://www.ncbi.nlm.nih.gov/pubmed/16002798