Tasty, processed food with irresistible combinations of carbohydrates and fat, overrides our normal appetite regulation and makes us overeat. This energy overload leads to weight gain (in susceptible people), insulin resistance, and metabolic dysfunction (1), and increases the risk of type II diabetes, fatty liver disease, cardiovascular disease, cancer, and even dementia. But you can prevent or reverse these processes with one simple strategy: Eat minimally processed foods.
Surprisingly, and contrary to popular rhetoric, diets high in either carbohydrate (even refined carbohydrate) or fat won’t make you overeat. In fact, the opposite is true. (2; 3). Problems arise, however, when refined carbohydrates and fat are combined in processed food.
Eating fat or carbohydrate causes the release of dopamine in the brain, which increases the drive to eat. This was an essential survival adaption throughout most of evolution. But combining fat and carbohydrate (which is unusual in nature) magnifies the rewarding effect (4). We can all intuitively understand this. How excited do you get about eating plain white bread? Or melted cheese on its own? How about if we throw them together, with tomato and seasoning, to make a pizza?
Processed foods with tasty combinations of fat and carbohydrate, such as chocolate, pastries, pizza, ice cream, and take-away food come top of the rankings for cravings and addictive eating behaviour (5; 6; 7). There are several factors at play here, but the most problematic may be the processing itself (8). Ultimately, the better food tastes, the more we eat of it (9; 10). And having ready access to processed fat- and carbohydrate-rich foods drives overeating and very rapid fat gain (11). Here again, the processing itself appears to be the dominant player (12).
When we consume energy – from carbohydrate or fat (or protein for that matter) – our working tissues (muscles, organs, etc.) take what they need for maintaining life and fuelling activity, and the remainder is stored as fat. However, if we have a sustained energy overload, at some point we reach our individual fat storage capacity, which is largely genetically determined (13). When this happens, levels of sugar and fat rise in the blood. They have nowhere else to go. The cells in working tissues are already full of energy. Letting more in would be harmful, even lethal to the cells (14). So, various mechanisms are employed to prevent both fat and sugar from entering the cell. This is referred to as ‘insulin resistance’, because it looks like cells are not responding to insulin’s signal to take in more sugar.
Overeating, therefore, causes energy overload and insulin resistance (15; 16). And insulin resistance is a strong predictor of metabolic diseases such as type II diabetes, cardiovascular disease, and cancer (17).
Let’s be clear about something here: It’s not all about body weight, BMI, or even body fat. It’s well established that being overweight or obese (in BMI terms) is associated with insulin resistance, metabolic dysfunction, and poor health outcomes (18). But, up to 30-40% of obese people are metabolically healthy and have more favourable health outcomes (19). In addition, as many as 20% of normal weight people are metabolically unhealthy (20), and have the same health risks as their overweight and obese counterparts (21). This is because total body fat is not the culprit here. Visceral (or intra-abdominal) fat is (22). As visceral fat increases, so does insulin resistance and metabolic dysfunction, for both normal weight and overweight people (23).
How much fat is directed in to visceral stores is partly genetically determined (24). But diet quality is an important factor. For example, consuming sugar-sweetened beverages (i.e. soda) increases visceral and liver fat stores, and causes metabolic dysfunction, even without overall body fat gain (25). And the effects can be seen with low-moderate consumption in as little as three weeks (26).
So, whether you’re overweight or not, you may be (or may become) metabolically unhealthy. But why does it matter? Because metabolic dysfunction is very common (27; 28), and, if allowed to develop, it may wreck your quality of life (29), and shorten your lifespan (30).
If super-tasty, processed food is causing us to overeat and putting our metabolic health at risk, there is a straightforward solution: Eat minimally processed food. It sounds too simple, doesn’t it? But it really works. A diet of minimally processed food causes a dramatic reduction in calorie intake, and significant weight and fat loss, in as little as two weeks (31). Even when there is no calorie restriction. And it does this independently of fat, carbohydrate, protein, sugar, fibre, and salt content. Calorie reduction and weight loss is an effective way to reduce visceral fat (32), and thereby improve metabolic health (33).
Minimally. Processed. Food.
It’s the reason why seemingly diametrically opposed diets – such as low-carbohydrate diets and low-fat diets (34), plant-based diets (35) and paleo diets (36) – are all effective at reversing energy overload and restoring metabolic health.
(By the way, exercise is also important here (37). But we’ll get to that another time.)
Let’s clarify what minimally processed food means. There are three aspects to consider:
- Avoid all ‘ultra-processed’ food, such as pizza, ice cream, breakfast cereals, biscuits, soda, and crisps, and other packaged, ready-to-eat convenience foods. (This may seem obvious, but it’s difficult because this food has become so normalised (38)).
- Prepare most meals and snacks from fresh, unprocessed ingredients. But limit the amount of processing you do. The further you take food away from its natural state, the more desirable it becomes. Potatoes are very filling, but when you remove the skin and mash them with butter, cheese, and salt, they’re hard to stop eating. Cooking chicken with oil, vegetables, and spices, and serving it with white rice and garlic naan bread, is very different to having simple grilled chicken with vegetables.
- When you do buy processed food, choose the least-processed version. For example, an artisan, high-cacao dark chocolate bar is far less processed than an industrially produced, high-sugar milk chocolate bar. Raw-honey from a local producer is very different from the honey-coloured syrup you find in most supermarkets. Raw, unsalted nuts are minimally processed (particularly if they’re still in the shells), dry-roasted peanuts are not.
This doesn’t mean food has to be completely bland and boring. You don’t have to do much with high-quality, fresh ingredients to make them sing! Although you may need to reset your palate slightly.