Are All Calories Equal?

16 February 2021
By Jack Coxall

Are All Calories Equal?

‘Calories in versus calories out’ is often quoted as a fundamental law of weight loss, but in reality it should perhaps be considered more of a starting point. It is true that an energy deficit is necessary to lose weight, therefore calorie intake is relevant. Unfortunately, in practice it becomes a little more complex.

‘Calories in versus calories out’ holds true when applied to an ‘isolated system’ eg. an experiment carried out in a laboratory setting. In such a system, burning 1,000 calories of spinach and 1,000 calories of muffins would release the same amount of energy. However, the human body is not an ‘isolated system’. There are a multitude of factors that determine how our body uses the calories we consume, including (but not limited to) our activity level, body composition and hormones.

Typically when determining a person’s Basal Metabolic Rate or BMR (the number of calories needed to keep the body functioning at rest) and their Total Daily Energy Expenditure or TDEE (the BMR multiplied to account for activity level) a formula, such as the Harris Benedict equation,  will be used. While this works fine as a starting point, as a concept ‘calories in’, is incredibly difficult to accurately predict or measure. This is due to factors such as thyroid and steroid hormone status and mitochondrial efficiency making differences in food absorption hard to account for. It’s even more difficult to predict how nutrients are distributed (whether to muscle, glycogen or fat) following absorption.

The human body simply does not respond to every calorie you consume in the same way. The macronutrient balance of the food you eat can have a significant impact on your hormones which will influence how your body processes calories. For example, consuming protein can help to keep blood sugar and insulin levels steady, which releases hormones that can curb appetite. Whereas consuming carbs can cause fluctuations in insulin and other metabolic hormones, leading to hunger. Protein also requires the body to burn a lot more calories during digestion when compared to how it digests carbohydrates. Similarly, some fats stimulate the burning of calories. Omega-3 fats increase the process of uncoupling proteins, which raises the temperature of the body leading to excess calories being burned. It is therefore possible to adapt how many calories your body burns by adjusting the macronutrients you consume, without changing total calorie consumption. The consumption of carbohydrates, particularly those with a higher glycemic index, will increase the body’s level of insulin. If insulin levels become chronically elevated, cells become resistant to it. This drives up the ‘stress hormone’ cortisol, which will most likely lead to fat gain.

When considering the ‘calories in versus calories out’ debate, particularly where it pertains to weight loss, it’s worth considering a fundamental question: what drives us to eat? It’s not a trick question, the answer (on the surface at least) is simple: hunger. Eating in a way that curbs your hunger effectively is going to be a more successful weight loss strategy in the long term. Keeping your hunger, energy and cravings in check should rank as a high priority when it comes to weight management. These factors can act as an indicator that your metabolism is in balance and if it is, you’re less likely to struggle to achieve a calorie deficit.

An important factor to consider is how satiating the calories you consume are and how effectively they curb your hunger. Foods higher in protein tend to be more satiating than carbohydrates, particularly simple carbs. 100 calories of a chicken breast is likely to keep you feeling fuller for longer than 100 calories of sweets, it’s also less likely to lead to an initial spike in energy followed by a rapid crash. Refined, or simple, carbs are absorbed and digested rapidly, raising blood sugar quickly and insulin. The elevation of insulin levels causes a crash in blood sugar which leads to cravings of more simple carbs to bring things back into balance. This leads to overconsumption as the body becomes stuck in a loop- the consumption of refined carbs leads to cravings for more refined carbs.

Relying solely on calorie restriction, without paying attention to keeping your hunger, energy, cravings and metabolism in check, is not the optimal strategy for long term weight loss and management. Putting this theory in practice, the New England Journal of Medicine conducted a study wherein overweight individuals were put on a diet of 550 calories per day for 10 weeks. During this time of severe calorie restriction, they displayed elevated levels of ghrelin, which stimulates hunger, and of gastric inhibitory polypeptide, which promotes fat storage. Conversely, the hormone leptin, which suppresses hunger and promotes fat burning, was significantly reduced during the ten week period and remained that way for the remainder of the one year study. Following the ten week calorie restriction, participants lost an average of 30 pounds. However, over the course of the year, they regained an average of 15 pounds.

‘Calories in vs calories out’ can be considered a good starting point in terms of understanding how what we consume impacts our bodies. It’s a relatively simple concept, making it easy to understand and apply to lifestyle changes for those new to weight management. However, it is something of an over-simplification. For long term progress it is important to understand the way in which calories from different sources differ in terms of how our body processes them. With this understanding, you’re setting yourself up for consistent, long term results rather than getting stuck in a cycle of yo-yo dieting.


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