Diets Debunked

I hear this all the time: calories in vs calories out. Burn more calories than you eat. That’s all you need to know when it comes to weight loss.

Technically, that is true; as long as you arein a calorie deficit you will lose weight. However, a calorie doesn’t always equal a calorie. Let’s talk about it.

The Basics of Calories

First, let’s start with the basics. A calorie is a unit of energy. In the context of nutrition, calories refer to the amount of energy that macronutrients provide to our bodies. As an example:

• 1g fat: 9 kcals
• 1g alcohol: 7 kcals (yes, alcohol is a macronutrient)
• 1g carbs: 4 kcals
• 1g protein: 4 kcals

So we can see, protein and carbs contain the least calories and are neck and neck in terms of the calories they provide, followed by alcohol and then fat. However, this is a bit of a simple view of things and doesn’t take into consideration the way our body breaks down and processes nutrients.

The Thermic Effect of Food

One of the key nuances in measuring calories is the thermic effect of food (TEF). TEF refers to the energy required to digest, absorb, and metabolise the nutrients in our food. Different macronutrients have different thermic effects, meaning different nutrients burn more calories than others:

• Proteins: Proteins have the highest thermic effect, requiring about 20-30% of their energy content for digestion and absorption. This means that if you consume 100 calories of protein, your body will use 20-30 of those calories just to process it. That means for every 4 kcals protein you are consuming, you’ve netted only 3 kcals.
• Alcohol: Alcohol has a slightly lower thermic effect than protein, with about 15% of energy content being used for digestion. This means for every 10 kcals of alcohol you drink, you only net 8.5 kcals.
• Carbohydrates: Carbohydrates have a moderate thermic effect, using about 5-10% of their energy content for digestion and absorption. This means for every 10 kcals carbs you’re eating, you net 9 kcals.
• Fats: Fats have the lowest thermic effect, requiring only about 0-3% of their energy content for digestion and absorption. This means for every 100kcals fat you eat, you net 97 kcals.

Therefore, for every 100 calories of each macronutrient you consume, you absorb:

• 97 calories from fat
• 90 calories from carbs
• 85 calories from alcohol
• 70-75 calories from protein

This means that not all calories are created equal when it comes to the energy required to process them. Protein is theoretically a lower calorie choice than all of the others, despite having the same calorie content as carbs, due to its thermic effect.

The Caveat With Carbohydrates

Another important factor to consider is the type of carbohydrates you consume, however.

Carbs can come in higher fibre varieties, and lower fibre varieties, but here’s the kicker; the carbohydrates on the label include the carbs coming from fibre, and they are typically counted as still providing 4 kcals/g. In reality though, the calories fibre are not fully absorbed, with only an estimated 2 calories per gram being absorbed into the body. Therefore, high fibre carbohydrates are typically lower calorie than they appear on the label, due to us being unable to elicit half of the calories they contain.

Bioavailability of Calories

The concept of bioavailability is crucial when discussing the nuances of calories. Bioavailability refers to the proportion of a nutrient that is absorbed and used by the body. Not all calories in food are equally bioavailable, and this can vary depending on the type of food and its processing.

Ultra-processed Foods vs Whole Foods

Ultra-processed foods, such as ready meals, sugary snacks, and fast food, often have a higher calorie content and lower nutritional value compared to whole foods. However, the calories in ultra-processed foods are often more bioavailable, meaning that your body can absorb and use them more easily. Research suggests that the calories from an ultra-processed food with a very uniform, smooth and squishy texture (like a white bread PB&J) can be absorbed 40% more efficiently than those calories from a non-processed variety that is tougher and harder to digest. Therefore, although they may be the same calorie content on the surface of it, you’ll likely absorb more calories from the UPF variety.

Whole foods, such as fruits, vegetables, whole grains, and lean proteins, typically tend to have a lower calorie density and higher nutritional value. The calories in whole foods are often less bioavailable due to their natural fibre content and the presence of other compounds that can inhibit absorption. This means that even if a whole food has the same calorie content as an ultra-processed food, your body may absorb fewer calories from the whole food.

The Role of Cooking and Processing

Cooking and processing can also affect the bioavailability of calories. For example, cooking can break down the cell walls of plants, making their nutrients more accessible to the body. Processing (such as blending, mixing or mincing) also allows a more homogenous texture, meaning our body does not have to work as hard to break down the food. This means more calories are absorbed from the same food.

Practical Implications

So, what does all this mean for your diet? Here are some practical takeaways:

1. Focus on Nutrient Density: Instead of just counting calories, focus on the nutrient density of your foods. Choose foods that are rich in vitamins, minerals, and other beneficial compounds.
2. Prioritise Whole Foods: Opt for whole foods over ultraprocessed foods. Whole foods tend to have a lower calorie density and higher nutritional value, making them a better choice for overall health.
3. Balance Your Macronutrients: Aim for a balanced intake of proteins, carbohydrates, and fats. Remember that proteins have the highest thermic effect, so including them in your meals can help reduce the total calories netted.
4. Choose High Fibre Carbohydrates: Opt for high fibre carbohydrates, such as whole grains, fruits, and vegetables, over low fibre carbohydrates. High fibre carbohydrates also provide a steady release of energy and have a lower impact on blood sugar levels.
5. Be Mindful of Cooking Methods: Pay attention to how you cook and process your foods. Gentle cooking methods, such as steaming and baking, can help preserve the nutritional value of your foods, whilst reducing the ease in which your body can elicit the calories from the food.

Overall, the idea that a calorie is just a calorie is an oversimplification that ignores the complex ways in which our bodies process different types of foods. The thermic effect of food, the type of carbohydrates, and the bioavailability of calories all play a crucial role in determining how our bodies use the energy we consume.

As a dietitian, I encourage you to look beyond the calorie count and focus on the quality of your diet. By choosing nutrient dense, whole foods and balancing your macronutrients, you can support your overall health and well being in a way that simple calorie counting cannot achieve.

Photo source with thanks.