Not All Calories Are Equal
Quantifying calories is still the principle target for intervention in preventing or treating obesity and related diseases. This thinking assumes that all calories have the same effects on weight, regardless of their source. However, it isn’t as simple as that.
Fats, Protein and Carbohydrates – Different Functions, Different Effects
Calories are measured by calculating how much heat a food gives off in an oven. But the human body is far more complex than an oven. The journey from fork to toilet may take anywhere from 8 hours to several days. Protein and carbs have the same number of calories gram for gram but the body uses them in different ways.
Let’s look at the how the 3 macronutrients, protein, fats and carbohydrates, affect body function:
Calories from Protein
Dietary protein promotes satiety, thermogenesis, energy expenditure, and changes body-composition in favor of fat-free body mass (1,2). Protein is used for building bone, hair, skin, nails, muscle and other body tissues. It can serve as fuel for the body in the absence of other energy sources. It is less likely to be stored as fat on the body.
Calories from Fat
Fat in food breaks down slowly so it will keep you feeling full for longer. Fat is used for making hormones and neurotransmitters and to protect our nervous system and internal organs. It is also a key way that the body stores energy in times of plenty ready to use in times when food is scarce. We are still programmed to store excess fuel for times of famine but, for most of us, the famine never comes.
Calories from Carbs
All carbohydrates break down into sugar, mainly glucose, which is the body’s main source of fuel. Simple carbs from processed and sugary foods break down fast and are rapidly absorbed into the blood stream causing a blood sugar high. This leads to a release of insulin to take the sugar from the blood into the liver, the muscles and the cells. However, if a lot of sugar ends up in the blood these storage sites become full and the excess sugar is converted to fat for long term storage. After the blood sugar high there is a slump which leads to tiredness and hunger and the need for another sugary pick me up. It’s a viscious cycle of being overfed but undernourished.
Complex carbohydrate break down into sugar more slowly meaning you get a steady trickle of sugar into the blood stream providing energy over a longer period of time.
Our ancestors had to work hard to find sugary foods and they weren’t available all year round. Now we can access huge amounts of sugar without expending any energy.
Time to Move On From Calorie Counting
Calorie counting is an appealingly simple way of measuring food intake. But calories tell us nothing about how satiating a food will be or its effects on metabolism, insulin, energy or body function.
Calorie based thinking is inherently biased against foods high in fat and supportive of carbohydrate rich foods and those containing artificial sweeteners. There are many healthy whole foods that are high in beneficial fats that have positive effects on both weight and health that get demonised along with less healthy foods containing processed fats.
Counting calories can lead to poor food choices and disrupts the ability to tune into what the body’s hunger and fullness signals. Obesity and related diseases are often best looked at as problems of neuro-hormonal pathways that are not addressed by calorie counting. Researchers suggest that public health should promote the consumption of whole foods that help protect against obesity and metabolic dysfunction and not continue to promote calorie-directed messages that may exacerbate epidemics of obesity and related diseases (3).
1. Madsen L, Myrmel LS et al. Dietary Proteins, Brown Fat, and Adiposity. Front Physiol. 2018 Dec 12;9:1792.
2. Drummen M, Tischmann L. Dietary Protein and Energy Balance in Relation to Obesity and Co-morbidities. Front Endocrin (Lausanne). 2018 Aug 6;9:443.
3. Lucan SC, NiNicolanaonio JJ. How calorie-focused thinking about obesity and related diseases may mislead and harm public health. An alternative. Public Health Nutr. 2015 Mar;18(4):571-81.