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Does a Calorie Equal a Calorie?

Calories in Greek yogurt

This question crops up a lot amongst nutritionist as there are two potential right answers.

On the one hand, if you were to compare 100 calories of fat, protein and carbohydrates against each other – in a thermodynamic sense – then yes they are equal to each other as they release the same amount of energy when exposed to a Bunsen burner.

However, throw in the human body and this sense of equality is quickly lost.

Part of the problem stems from the fact that different foods influence your satiety, metabolic rate, blood sugar levels, brain activity and the hormones responsible for fat storage, in different ways. Meaning the way your body responds to carbohydrates is different to that of proteins.
Similarly, they are not always absorbed in the same way. For instance, if over the course of a day you consume lots of high fibre foods (nuts, vegetables, etc.), then of the calories consumed from these foods, only three-quarters would actually be used by your body. The rest would simply be excreted as waste.

And this is a scary thought, as in a world where we are taught to calorie count and rely on food labels; the reality is - what you are eating (calorie-wise) isn’t always what your body is getting.

What makes calories unequal to each other?

The answer is simple: the thermic effect of food.

Now if you’re unfamiliar with this term, the ‘thermic effect of food’ is essentially a measure of how much different foods increase energy expenditure (due to the amount of energy needed to digest, absorb or metabolise nutrients).

Bearing this in mind, if we were to apply this definition to our examination of the metabolic pathways of proteins, carbohydrates and fats; then it would quickly become apparent that some – carbohydrates and fats - are more efficient than others –proteins - at using the foods energy within the body and not losing it as heat.

Protein is considered the least efficient, because of the 4 calories protein contains per grain; the majority of it is lost as heat when metabolised by the body. This means of the three: protein requires a lot more energy to metabolise than carbohydrates and fats.

Still confused by what this means? Let me make it a bit clearer for you by showing you the thermic effect of carbohydrates, fats and proteins:
  • Fats: 2-3%
  • Carbohydrates: 6-8%
  • Proteins: 25-30%
Now, if we were to work on the premise of protein having a thermic effect of 25% and fats 2%, this means if you had 100 calories of protein, you would effectively end up with only 75 calories; whilst if you had 100 calories of fat, this would end up as only 98 calories.

Get the picture? Their calories might be the same on intake, but once your body gets involved the amount of calories your body actually absorbs can prove substantially different.

Yet even within fats, carbohydrates and proteins themselves, not all of their calories are equal. Especially in the case of carbohydrates (as we’ll prove in a moment):
  • Fats considered a great source of energy, fats contain 9 calories per gram and have been proven to slow down digestion; deliver fat-insoluble vitamins to your body, and provide important building blocks to your cells.
Naturally some fats are better for your health than others. Polyunsaturated omega-3 fats (wild salmon, flaxseed, etc.) contain anti-inflammatory properties, whilst artificial trans fats can increase inflammation and your chances of heart disease.
  • Protein reputed to keep you fuller for longer (as it slows down digestion), protein is essential for the maintenance and creation of new cells. It is also beneficial during weight loss as it can increase your satiety and offset the amount of lean muscle that is burned for energy during a calorie deficit.
Proteins typically contain 4 calories per gram, but like fats there are different levels of protein quality, some of which are better for the body than others. Higher quality proteins can reduce your appetite and optimise muscle repair/recovery; whilst lower quality proteins (found in hamburger meat) have been linked to metabolic disease and insulin resistance, due to the amount of branched-chain amino acids they contain.
  • Carbohydrates of the three, carbohydrates have the biggest issue with differentiating calories, as our bodies use the various carbohydrate types (fiber, starch and sugar) in different ways.
Carbohydrates are typically used as a quick source of energy by your brain, liver and muscles, and aside from fibre (which can’t be digested by the body) they provide 4 calories per gram.

Like fats, there are differing quality levels of carbohydrates:

 - Fibre – although not a source of calories, it is a high quality carbohydrate as it helps to slow digestion and moderate the absorption of other nutrients such as sugar.
 - Sugar – even within sugar their calories differ. Take the case of glucose and fructose. Starchy foods such as rice, potatoes and pasta are predominantly made up of glucose which is a simple sugar that is easily burned for energy by the cells in your body. Stored in your liver and muscles, glucose is a quick source of energy when you exercise or sleep; however, should you consume too much it can lead to weight gain and the accumulation of subcutaneous fat (less harmful fat). Fructose (found in fruits, syrups and sweeteners) on the other hand, can only be broken down by your liver, and when consumed in high quantities, can end up overwhelming your liver, and contributing to liver disease and insulin resistance.

As you can see, even within their own groups not all calories are equal. As a result, it is important that you take care when managing your diet and of those around you as reading a label is not enough.

Luckily you can easily improve your knowledge of foods and nutrition with the help of our Advanced Nutrition and Health Level 3 course. In this one compact course, you can feed your curiosity and acquire a deeper appreciation for the impact different food types can have on your body.

Alternatively, you can visit us at Association of Learning and turn this passion for health eating into a credible career.

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