Why Weight Loss Isn't As Simple As Calories In Vs Calories Out

With over 26% of UK adults and 1/5 of our children leaving primary school obese it’s clear we’re dealing with an obesity crisis. We often hear people claim that if you eat less and move more you’ll solve the problem. Although, this is an incredibly reductionist view, it really isn’t quite as simple as that and here’s why…

1. Appetite and weight management
Our appetite signals are incredibly powerful, they’re there to notify us when we’re hungry and satiated. Grehlin (the hunger hormone) appears to be very effective and reliable at letting us know when we’re hungry but when it comes to Leptin (the satiety hormone) our environment can often override this. I’m sure we can all relate to the time we went in for another serving of dessert or picked a snack off the checkout aisle because our environment drove us to do so. Research also suggests that chronic over-consumption can stimulate a constant desire for hedonic rewards making resisting food extra challenging. What’s more is that hunger hormones have been shown to increase in response to weight loss, making weight maintenance even more challenging.

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2. Maternal influence on infant nutrition
Studies have shown a relationship between mothers who smoke during their pregnancy and an increased risk of obesity in the child in later life. The same has been shown for mothers who have a poor diet during the first and second trimester but interestingly no association was made between obese offspring and mothers who have a poor diet in the third trimester. Although conversely, mothers who were exposed to famine during their pregnancy led to the offspring with increased health complications later on in life. Evidently, the maternal diet plays a considerable role in the offspring’s weight management and health related complications later on in life.

3. Nutrition labeling
With so much information of health and nutrition in the media it can be incredibly challenging to identify the truths from the myths. The regulations on nutrition guidance on packaging has become more complicated to understand and latest research shows that whilst 50% of shoppers use it in-store, only 20% use it online and considerably less actually understand what it means.

4. Bioavailability of nutrients
Bioavailability is the amount of the nutrients which can be absorbed and utilised within the body. Whilst a food may contain x amount of energy (denoted as calories) if the full amount of energy cannot be released from the food it may have an affect on weight. As an example, foods with a low glycemic index may have a significantly lower release of energy as some fibres create a coating around food particles inhibiting the release of energy. In one study chickpeas showed to release less energy than wheat particles. The factors which determine this include: whether the particle separate (detach from other particles) or fracture (briefly split), permeability of the cell wall, cell size, shape and thickness and the type of fibre. Other research suggests that fat released from almonds is limited as only the first layer ruptures to release the fat during digestion. The remaining fat is excreted via stools.


Furthermore, some processing techniques may increase the availability of starch in certain foods, consequently increasing glycemic index. Therefore, this theory works both ways; it is possible to significantly increase the bioavailability of energy by changing its state. This suggests that not all calories are utilised equally.

It’s also important to note that in relation to weight loss this is an interesting area although we should also be concerned about micronutrients not being absorbed as a result of cell walls inhibiting their release.

5. Adaptive thermogenesis
Adaptive thermogenesis refers to the amount of heat produced (or energy used) in response to environmental changes in body temperature and diet. Research shows that our resting metabolic rate (the amount of energy you burn at rest with no activity) decreases following weight loss of 5% body weight or higher. This means that where you might have required 1300kcal at rest you may only require 1200kcal at rest (these figures are examples). Therefore that extra 100kcal that you’ve been consuming now becomes a surplus. Stick with me…

Furthermore, adaptive thermogenesis decreases after 10% of body weight loss. This often occurs as a result of a calorie restriction which causes your metabolism to slow and therefore reduces the amount of calories you utilise making it even harder to lose weight.

There you have a few key reasons as to why suggesting that weight loss isn’t as simple as calories in< calories out. This isn’t to suggest that weight loss isn’t achievable at all it’s to draw your attention to such a highly complex area which is very often limited to a single equation.