The Psychology of Nutrition | Psychology Today

Source: Deva Darshan/Unsplash Most people are aware that in order to lose fat, we need…

The Psychology of Nutrition | Psychology Today
Deva Darshan/Unsplash

Source: Deva Darshan/Unsplash

Most people are aware that in order to lose fat, we need a calorie deficit i.e. to burn more calories than we’re taking in. Weight change is therefore influenced by the amount of energy you consume and the amount of energy you expend.

The scientific literature shows that caloric reduction is more likely to lead to significant weight loss than solely increasing your exercise levels. What you eat is fundamental and plays a larger part in losing weight. Essentially you can’t outrun a poor diet. 

However, the research also shows that physical activity plays a critical role in maintaining weight loss. Low levels of physical activity are associated with a three-times greater risk of major weight gain in men and nearly a four-fold higher risk in women. Furthermore, the health benefits linked to exercise are bountiful: improved mood, self-esteem, energy levels, cardiovascular fitness, and stamina, and lower risk of depression, stroke, hypertension, heart disease, Type 2 diabetes, dementia, osteoarthritis, certain cancers, and early death. The Academy of Medical Royal Colleges has described exercise as a “miracle cure.”

So what’s the bottom line? Sustainable weight loss and long-term mental and physical health is more likely to be attained by making changes to your dietary intake and physical activity. In this post, we will take a look at where you should direct your attention when it comes to nutrition and sustainable weight loss. 

What nutritional changes should I make?

As we covered in my last post on sustainable weight loss, there is clear and consistent evidence that diets typically are ineffective in the long run. The flaw with most diets is that they’re rigid and restrictive short-term measures. We can temporarily cut out entire food groups and adhere to specific diet regimens, but we’ll likely return to our previous ways of eating. 

Most diets demonise carbohydrates or fats. However, carbs, fats, and proteins are all macronutrients—nutrients that are required in large amounts in the body. In short:

  • Carbohydrates are an excellent source of energy to support the brain and bodily functions, help preserve lean muscle mass, and improve digestive health.
  • Fats provide energy, are a source of essential fatty acids (i.e., that the body cannot make), help cells absorb vitamins A, D, E, and K, and support cell growth. 
  • Proteins are considered the building block of life, as they are involved in the repair, maintenance, and growth of cells.

While we’ll likely have to make dietary changes to achieve a calorie deficit, most people focus solely on the quantity (or the number of calories) of macronutrients (‘macros’). Carbohydrates and proteins provide about 4 calories (4kcal) per gram, and fat provides 9 calories (9kcal) per gram. However, a common psychological mistake is to overlook the quality of the foods. Not all macros are created equal. 

Focus on quality

The type of carbohydrate, fat, or protein you eat is just as important, if not more so, than the quantity. Some sources are healthier than others, and so lend themselves to better health and weight loss. Most foods contain all three macros but are predominantly associated with one. For instance, we often refer to meat as a protein, and yet it also contains fat. Rather than initially cutting down on a specific macro, shift your focus to improving the quality of the foods you eat. You probably already know what healthy choices look like, but just in case there’s any doubt, here’s a brief science-based guide:


  • Healthier sources: vegetables, fruits, whole grains (e.g., whole wheat, oat, quinoa, brown rice, rye, barley) and legumes (beans and peas).

Healthier sources contain more vitamins, minerals and fibre, are digested more slowly, and sustain your energy for longer. A metabolic study from Harvard compared eating mainly low glycaemic index (GI) carbohydrates (i.e. whole grains and beans, which are digested more slowly and cause a gradual rise in blood sugar levels), with higher GI carbs (e.g., white rice, white potatoes, sugary cereals). With low-processed low GI carbs, people’s bodies burned significantly more calories than on a high GI diet, even though they consumed the same number of calories and did the same amount of physical activity. On average individuals burned about 126 calories more per day when eating lower GI compared to higher GI carbs. This is the equivalent of walking for about 30 minutes every day. Not all calories are the same from a metabolic perspective. One of the authors of the study concluded: “the quality of the calories going in affects the number of calories going out.”

  • Unhealthier sources: more processed and refined foods, such as cakes, cereals, white bread, pastries, sugar-sweetened drinks etc.

These foods tend to have a high GI: they are broken down more easily, causing spikes in our blood sugar and insulin levels. This does not mean that we will never eat these foods, but consuming them on a daily basis can increase hunger and the likelihood of overeating. In the long-term, the risk of weight gain, heart disease and diabetes rises too.  


  • Healthier sources: foods that contain healthy unsaturated fats i.e. monounsaturated and polyunsaturated fats. For instance, tree nuts (e.g., almond, walnut), seeds (e.g., sunflower, flaxseed, chia, pumpkin), legumes (e.g., peanut, chickpeas), avocado, vegetable oils (e.g., canola, olive) and oily fish (e.g., salmon, mackerel, anchovies, sardines, herring).
  • Unhealthier sources: processed, baked or fried goods, including biscuits, cakes, cookies, French fries, pastries, pies, pizza, burgers etc. 


  • Healthier sources: fish, lean poultry, legumes (beans and peas e.g., black, garbanzo, pintos, split peas) and nuts. Fish and plant-based protein sources can lower harmful (LDL) cholesterol levels. 
  • Unhealthier sources: red meat (e.g., beef, lamb, pork) and processed meats (e.g., bacon, deli meats, ham, sausages), which contain more calories and saturated fats than white meat. High intakes are associated with an increased risk of colon cancer, diabetes, and heart disease. 

Shifting Your Mindset

Research shows that weight gain is most strongly linked to our daily eating habits, as opposed to overeating when we’re dining out. It’s unrealistic to expect yourself to forgo eating chocolate or pizza for the rest of your life. As we covered in the previous post, studies show that banning a food actually backfires, making it more desirable. A more useful mindset is to think in terms of ‘everyday foods’ and ‘sometimes foods.’ The key is to focus on improving the quality of your daily breakfast, lunch, snacks, and dinner. By creating a healthy overall pattern of eating, you can still enjoy that slice of cake or pizza when you really feel like it. 

Finding Your Sustainable Balance

In terms of weight loss research, when comparing groups assigned to low calorie diets with different macronutrient proportions of carbs, fats and proteins, groups generally lose (and regain) similar amounts of weight on average, especially when comparing the results after two years. Researchers from the University of Toronto and Stanford University analysed the results of 48 randomised controlled trials into diet programs. What did they conclude? “The ideal diet is the one that is best adhered to by individuals so that they can stay on the diet for as long as possible.” Long-term weight loss is about making long-term, sustainable changes that suit you. 

The research is even more fascinating when you look more closely at the data. Within a research group, some people initially lose weight on a specific diet (which we would expect), while others actually gain weight. One study revealed that in the same group assigned to a low carb diet, one person lost over 40 pounds while another participant gained over 30 pounds. In the low-fat group, the range spanned from losing over 25 pounds to gaining over 25 pounds. A difference of over 50 pounds among those instructed to follow the same diet.

Tailored Nutrition

How an individual responds to a pattern of eating depends on that person’s genetics, personality, preferences, and lifestyle. What works best for you may differ to your partner, neighbour, or work colleague. Unfortunately, there is no one-size-fits-all solution. Your task is to find a healthful way of eating that is sustainable and enjoyable for you! Remember, an energy deficit does not have to equate to an enjoyment deficit. Rather than focus on foods that you want to avoid, direct your attention at each meal to all the delicious, nutrient-dense options that you find tasty, will nourish your body, and leave you feeling satisfied. 

If you’re still unsure about proportions, the ‘half-plate rule’ is a simple and healthy place to start. Whenever you can, fill half your plate with vegetables (and fruits), a quarter with healthy protein, and a quarter with high-quality carbs. A useful visual representation is the Healthy Eating Plate, designed by nutritional experts at the Harvard School of Public Health. 

*This post has been prepared from information in Dr. Aria’s contributing chapter, “The Psychology of Health-Related Behaviour Change,” in the medical book A Prescription for Healthy Living (Elsevier Publishing, 2021).