Can the method used to measure calories become inaccurate? Read to discover!
Some people count calories to lose weight, but how accurate are we in doing so?
The fundamental principles of nutrition have for long used calories as a familiar unit of energy. The aim has always been to accurately record what was eaten and how much of it we spend in our day. It might seem simple, but it’s not. We usually tend to underestimate the amount of food we eat –I must admit I’m one of those that cheat in the calorie-tracking apps–: forgetting some meals or drinks, not being accurate with the size of the portion eaten, etc. But even if we were accurate in our records, it is not always easy to match the actual content of those foods with the data existing.
The calories in labels try to quantify the metabolizable energy from food, this is not actually measured in a lab, they are calculated knowing how much energy giving the ingredients are instead. We use the Atwater factors –dating from the 1900s– which determines fat at 9kcal/gram, alcohol at 7kcal/gram, protein at 4kcal/gram and carbohydrate at 4kcal/gram. However, the amount of energy absorbed still depends on the matrix and digestibility of that food.
And even if the Atwater factors were accurate, the concept of metabolizable energy does not take into account the energy cost of digestion, absorption and transportation of the food –the thermic effect of feeding.
Energy expenditure depends on the following factors:
- Metabolic rate: represents the calories that you burn while resting and fasting –and it represents 60-70% of the total energy expenditure.
- Physical activity: this is the most difficult factor to measure as it depends on a lot of factors.
- Thermogenesis: this is the energy cost of digestion, absorption and transportation of the food. This is not measured but assumed as a proportion of the total of the food and this varies for each food group –proteins can be up to 25% of the energy in that protein, fiber 10-15% and so on. Therefore, the composition of your diet influences energy gain from food.
How difficult to quantify is energy intake?
It is extremely difficult to quantify energy intake. The errors range from recording accurately the food to the actual composition information of each food.
If we were to measure the metabolic rate in a laboratory the margin for error could be 20-50kcal/day –pretty good. For normal people, it can be 100kcla/day or more. Physical activity is also very difficult to quantify.
To lose weight it is true that we need to eat fewer calories than you burn, but it is not always easy to measure accurately energy intake and expenditure. It is recommended to make sure the calories that you eat come from nutrient-rich foods and don’t focus only on the energy they are supposed to have.
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