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Are all calories equal?

Is 100 calories of chips the same as 100 calories of fish? First, in a literal sense, a calorie is always a calorie since it’s a unit of energy. Energy cannot be made or destroyed, only transferred from one state to another.

When discussing changes in body fat, this is most closely related to energy balance over time – that is, whether you are in a calorie surplus or a calorie deficit. So, the calories in the food you eat is the key driver of whether you gain fat or not. The first half of this DEXA information video clearly spells out what is required for fat-loss to occur (the second half talks about muscle gain).

However, not all calories are treated equally within the body. Some of the calories in the food you consume will be used to digest, absorb, and metabolise the rest of the food, and some will be burned off as heat. This is known as the ‘thermic effect of feeding’ (TEF).

Protein has a TEF quite a bit higher than carbohydrates and fats, meaning that, in simplistic terms, more of the calories are ‘burned off’, leaving fewer to get stored as fat. Therefore a higher protein intake can be advantageous.

• Fat provides 9 calories per gram, and its TEF is 0–3%
• Carbohydrate provides 4 calories per gram, and its TEF is 5–10%
• Protein provides 4 calories per gram, and its TEF is 20–30%

A higher protein diet can also suppress appetitepreserve muscle mass and reduce food intake in real-world conditions.

Whilst a high-protein diet has this metabolic advantage, foods of all types that are more satiating (filling) can make sticking to a calorie deficit easier. 

Based on research on the satiety index, food volume, fibre, and water content all appear to influence how filling a food is. Examples of some of the top ranked foods in this study included potatoes, fish, oats, and oranges. 

By contrast, an ultra-processed diet (e.g. junk-type food) can result in a significantly higher calorie consumption. It may be wise, then, to limit  junk food to better control your calorie intake.

Regardless of a food’s TEF, to maintain weight, we need the energy equation to balance (energy intake = total energy expenditure).

Energy Intake (food & drink) = RMR + TEF + Activity Thermogenesis

Resting metabolic rate (RMR) is the amount of energy required to maintain the body’s most basic functions at rest. The conclusion to your first Bodyscan DEXA scan is providing a very good assessment of your RMR, using your unique DEXA data in what is known as the Katch-McArdle formula. The reason DEXA and Katch-McArdle beat the simpler formula you’ll find here (based on age, sex, weight and height) is that it uses lean mass as the main input, and lean mass (muscles and organs) is your body’s biggest energy burner.

The last variable in the above formula (Activity thermogenesis) refers to your energy expenditure from all activity. That is formal physical activity (eg, sport, training) as well as spontaneous activities such as fidgeting, maintaining one’s posture, walking etc. known as NEAT (non-exercise activity thermogenesis).

At your Baseline DEXA scan lasting one hour (or 80 minutes for two people; all UK DEXA prices here) we will use our experience to honestly assess your level of formal exercise as well as take account of unscheduled activity, such as step count, to arrive at overall energy expenditure.

Take-home: for fat loss, keeping body fat low and general health, design a varied diet with ample protein and fibre and one that is rich in micronutrients (vitamins and minerals). Protein and calories are really the only two numbers you need to keep tabs on. Don’t worry about other macronutrients, except the overall calories they provide, or other time-consuming distractions like meal-timing and glycemic indices.

Kevin Garde
Nutritionist and Bodyscan Consultant