What’s stopping you losing weight?
When you’re stuck in a loop of getting a handle on your eating, then it all goes to pot, you can start to feel hopeless about genuine, lasting change.
It’s not you
The problem is one of your biology interacting with our modern food environment. Differences between individuals mean that some of us are much more likely to gain weight than others. We would have varied like this over the entire course of human evolution, but the genetic differences only really showed through clearly once we entered an age of plentiful, cheap and energy-dense food.
It’s partly the food, but not in the way you may think
The buzz at the moment is generally around ultra-processed food, which appeals as an explanation for why we eat more. It’s relatively new, and there’s the spectre of the Big Food industry making billions from selling it to us, that paints a compelling picture.
But what is interesting, when you look at what the real experts are saying about research on why we overeat, the role of food processing is nowhere near as clear as it is portrayed in the media.
However shocked you are by this, or how much you want to resist the idea, it’s true that scientific research on ultra-processed foods is in its infancy. But there are very well-established findings, based on repeated studies of eating behaviour, that point to three main drivers of overeating. Irrespective of how processed the food is.
What are the Big Three?
A new review paper* has just been published, by one of the world’s leading research groups on eating behaviour. Professor Barbara Rolls and colleagues have summarised decades of studies which show that the proven factors that lead us to eat more are –
- Energy density
- Portion size
- Increased food variety
Let’s look at each one in turn, then what these facts mean for how you can manage your weight.
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Energy density
Let’s start with the biggie. Energy density – the number of calories per gram of food – has the greatest influence on our intake. Ways to reduce energy density include increasing fruit and vegetables, or decreasing the amount of fat, or adding water.
Without realising it, we tend to eat roughly the same weight of food on a daily basis. The weight of food we eat is more consistent than the amount of energy in it. This subconscious tendency has a big consequence for helping weight loss – you can leave the weight of food constant, and adjust the energy density of what you’re eating.
Tip: reduce the overall energy density of your meal by increasing the proportion of low-energy density components. Put simply, have half your plate made up of fruit and vegetables.
Tip: choose soup for enhanced satiation and delayed gastric emptying compared with same foods served as a regular meal. The addition of water, in the process of making the soup, reduces energy density and also changes how the food is digested.
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Portion size
Whether you’re aware of it or not, you eat more when you are served more. Particularly with foods that are higher energy density. So large portions of energy-dense foods override biological signals of fullness.
Tip: rethink VFM (Value for Money). It’s normal to think that getting more food for the same amount of cash equals greater VFM. But this equation falls apart if you eat all the food you bought at the bargain price, when you want to manage your weight. More food in a restaurant, or a supermarket serving, is great VFM if you are trying to GAIN weight. But if you want to lose kilos, don’t fall for saving pounds. Buy the actual amount that is right for you at this meal. If you do buy the bigger portion, leave the excess on your plate.
Tip: rethink food waste. This follows directly from the last point… if you are served more than you need, clearing your plate will scupper your attempts to shed pounds. The last mouthfuls – that you didn’t need – are no less wasted if they go through your body and into the toilet than if they go straight in the food recycling bin. If you eat them, your body will extract the calories and store them as fat, which won’t happen if the food goes in the bin.
Tip: use a takeaway box for leftovers at restaurants – studies show that when you have a to-go container, food and energy intake is reduced
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Variety
As you eat a particular food, the pleasurable taste you get declines over successive mouthfuls. But a different food, even if you’re starting to feel full, does not have this reduction in pleasure.
This “sensory-specific satiety” is a very well-established feature of the appetite system, and is thought to have evolved to promote the consumption of a range of foods, and therefore nutrients.
The problem is, that when we have lots of energy-dense foods on our plate, rather than a small number, we’ll eat more.
Tip: limit the number of foods on your plate at a single meal (get the variety over different meals in the week). And at a buffet, limit how many things you take.
Tip: if you are trying to increase your veg consumption, serve yourself a variety of different veg. Studies show that a variety of different veg lead to eating more of them overall, than if you just serve yourself your single favourite vegetable!
Tip: stock your food environment with a variety of nutritious low-energy-dense options, to help you resist tempting high calorie foods. And remember to put these in your line of sight.
The independent and additive effects of the Three
Each of the Big Three has its own independent effect on intake, as well as additively combining with the others.
So if you find it easier to focus on just one or two factors, they will have their own helpful effects.
Weight loss medication
It’s worth pausing to notice how what we’re talking about in this blog relates to medication.
Injectable weight loss drugs affect appetite signalling in the brain, and delay gastric emptying. They lead to reduced portion sizes being eaten, NOT because they have injected you with willpower, but because they increase satiety and delay gastric emptying. Food preferences change towards lower energy density, as they lead to reduced preference and cravings for high fat high sugar foods.
An alternative to weight loss jabs
If you are interested in an alternative to, or a complement to weight loss medication, knowing about the Big 3 can help you make changes to how you eat.
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Reference
* Rolls, B, Cunningham, P and Zuraikat, F (2025). “The Big Three” properties of food that drive intake. Physiology and Behaviour. https://doi.org/10.1016/j.physbeh.2025.114994
Photo by Ella Olsson for Unsplash