‘Calories In vs. Calories Out’ Doesn’t Work. Here’s Why
‘Calories In vs. Calories Out’ Doesn’t Work. Here’s Why

A nutritionist debunks the popular diet belief

As a nutritionist, one of the most common questions I have received is whether ‘calories in vs. calories out’ is true. Many — if not all — diet plans are based on this theory; you need to eat less and move more to lose weight. But is it the truth? Or is there more to it?

In this article we’re going to examine the calories in vs. calories out theory to ascertain whether it’s a good strategy for weight loss.

What is the calories in vs. calories out theory?

The calories in vs. calories out theory is known commonly in the health and fitness industry as IIFYM (if it fits your macros), a way of eating that solely focuses on how many calories are consumed and how many are metabolized through exercise.

However, other than IIFYM, the majority of diets you see in the health and fitness industry are based on the same calories in vs. calories out theory.

This theory argues that if you intake more energy (through food) than you expend (through exercise and daily movement), you will gain weight. If you intake less energy than you expend, you will lose weight. It’s all about energy balance.

What’s the science behind the theory?

Your body weight is regulated by energy balance. If you intake more calories than you expend, you will be in a positive energy balance which means your body isn’t able to regulate your caloric intake through expenditure, so you store more calories as fat with the intention of using them later, but rarely get used ‘later’ so just contribute to increasing amounts of adipose (fat) tissue.

If you have a negative energy balance you intake less calories than you expend so your body breaks down fat and muscle tissue stores to use for energy. This causes you to lose weight.

So what’s the catch?

In the diet and fitness industry, it’s all about calories and macros. While tracking macros and counting calories can be a helpful indicator as to how much you’re eating, it’s not a perfect science.

A calorie isn’t just a calorie. I often see infographics on Instagram with a picture of a McDonalds meal that is 250 calories vs. a healthy meal that is 500 calories with the caption along the lines of ‘just because it’s healthy doesn’t mean it’s low calorie’. Here are some examples of what I mean:

First of all — low calorie doesn’t mean healthy, these are not interchangeable terms.

Secondly — despite being higher calorie, the healthier meal is still preferred.

Even if weight loss is your goal, it’s ALWAYS better to choose healthier, nutrient dense, whole foods rather than lower calorie processed alternatives.

In general terms, calories in vs. calories out works. Plus, you need to be in a calorie deficit to lose weight, so it shouldn’t be totally discounted. However, if we want to get more specific — calories in vs. calories out is definitely not the full picture. Here are some examples why.

1. Exercise is an inefficient way to create a deficit

In terms of the calories out, many people focus on increasing their exercise activity to create a deficit. Many assume that their hour-long workout is going to put them in a significant energy deficit — because they burnt 500 calories according to their Apple watch — so they don’t even need to cut their calories! But in reality, exercise is an ineffective way to create an energy deficit.

Numerous studies conclude that exercise has, at best, a modest impact on weight loss but it’s less than most people believe. You really can not outwork a bad diet. The optimal way to lose weight is by combining a calorie deficit, clean diet, with increased exercise activity.

A 2012 randomized controlled trial (gold standard of research) lasting a year looked at whether diet, exercise or both combined was most effective for weight loss. The researchers found that the average weight loss was highest in the diet and exercise group (10.8% of body weight), compared to diet (8.5%) and exercise (2.4%).

A systematic review of intervention studies using exercise for weight loss, found that exercise energy expenditure had absolutely no correlation with weight loss. Numerous studies conclude that exercise has, at best, a modest impact on weight loss but it’s less than most people believe. So in terms of calories in vs. calories out — the calories don’t come ‘out’ as easily as you think.

As an example of this, if you have a ‘cheat day’ and eat 4,000 calories and try and work it off in the gym the next day, it’s not going to be possible. According to Harvard Health, a one hour weight lifting session burns only 224 calories for a 155 pound person. Plus, the more you workout, the more your appetite increases to recover.

If you’ve ever had an intense gym session you can probably relate to having an insatiable appetite post-workout, and often you might justify eating more because you ‘deserve it’. It’s never about restricting yourself post-workout, but if weight loss is your sole goal this method is not ideal— increasing your energy activity to try and create a deficit, but still eating more because you’re hungry — there’s clearly an issue.

The deficit has to be created from your diet.

Photo by John Arano on Unsplash

2. Calories are not all metabolized equally

All calories are not created equal. 100 calories of kale are not metabolized the same as 100 calories of candy. Because they’re different macronutrients right? Well, partly. Not only are different macronutrients metabolized differently — within the same macronutrient group, calories are metabolized differently. To explain this in action, here’s how sugars can be metabolized differently.

Carbohydrates are sugars that come in two main forms — simple and complex — depending on its chemical structure. Sugars can be categorized as single sugars (monosaccharides), including glucose, fructose and galactose, or double sugars (disaccharides) which include sucrose, lactose and maltose.

Fructose is the sugar you find in fruit, sucrose the table sugar you put in your coffee and glucose is found in carbohydrates like breads and pasta once they are broken down. The chemical molecules of the glucose, fructose and sucrose found in high fructose corn syrup (HFCS) are the exact same chemical molecules as the ones found in fruit. But they are metabolized differently by the body, which makes all the difference.

Fructose and glucose the two main simple sugars in your diet and gram for gram they provide the same number of calories, but the way they are metabolized in the body is worlds apart. Firstly, glucose is metabolized by all of your body’s tissues whereas fructose can only be metabolized by the liver.

When you consume too much fructose, your liver can’t keep up which leads to a fat accumulation in the liver, due to both increased lipogenesis and impaired fat oxidation. Too much fructose consumption over time causes non-alcoholic fatty liver disease (NAFLD), which is becoming more common in individuals of a normal weight due to the mass consumption of sodas.

So is fructose always bad? Well.. not exactly.

Fruit and food containing HFCS (like cereals, breads, pastas, salad dressings and a whole load more) both contain simple sugars, but they are metabolized differently, causing different effects on your health. The simple sugars in fruit are encapsulated in fiber and phytonutrients that slows down the release of sugar into your bloodstream. But the simple sugars in cereals do not contain the same nutrients, so cause a blood sugar spike and a whole range of issues. So if you eat 10g of fructose from fruit, it is absolutely not the same as eating 10g of fructose from soda.

Numerous studies have concluded that HFCS raises triglycerides and uric acid levels in the body, promoting the abnormalities seen in metabolic syndromes like hypertriglyceridemia. It contributes to high blood pressure and an increased risk of heart disease and obesity. It also affects your hormones, which leads us onto our next point…

3. Foods affect our hormones, which can affect how we use or store energy

Ghrelin, the hunger hormone, tells your brain when to eat and when to stop eating. Fructose increases ghrelin levels meaning it stimulates hunger despite satiety, which can not be stimulated by glucose. Glucose produces increases in circulating satiety hormones, making you feel full and to stop eating, whereas fructose does not.

A study by Angelopoulos et al found that high fructose corn syrup bypasses many of the body’s satiating signals like the hormones ghrelin and leptin that tell your brain when to start and stop eating. This promotes the overconsumption of energy, leading to weight gain and the development of insulin resistance and the resulting risk of type 2 diabetes.

To test this out, a study gave one group a fructose sweetened beverage and another group a glucose sweetened beverage and the same caloric intake for 10 weeks and unsurprisingly, the fructose group gained fat and decreased insulin sensitivity, whereas the glucose group did not.

As you can see, there’s a lot more to food than just their caloric density: the way they are metabolized, the hormonal response they stimulate, their glycemic index and so much more. Moreover, it’s clear that calories in vs. calories out isn’t the whole picture, and can’t be relied upon.

4. Our bodies burn different amounts of energy during digestion of macronutrients

Within the total amount of calories you burn in a day — known as your total daily energy expenditure (TDEE) — 15 percent accounts for the calories burnt during digestion. This is known as the thermic effect of food (TEF).

Protein has the highest thermic effect of any macronutrient, raising your metabolic rate by up to 30 percent. Carbs have the second highest — 5 to 15 percent are burnt, largely depending on whether they are complex or refined, and fat has the lowest — with less than 5 percent being burnt during metabolism.

Thus, if you compare a high protein diet with a lower protein diet — adjusted for calories — a higher protein diet causes a bigger spike in your basal metabolic rate and increases satiety throughout the day as it takes longer to digest, as shown in a 2004 study by Nutrient Metabolism. A higher protein diet will result in less energy storage, which over time can lead to weight loss, if a deficit is maintained.

5. We’re all counting calories and forgetting to count chemicals

Processed foods are filled with chemicals, fillers, trans fat and ingredients that are toxic to the body. FUN FACT: In Europe there are more than 1,300 chemicals that are not legally allowed to be added into food due to their toxic effect on human health. The US has only curbed 11 of these. Note: not made illegal, just recommended against.

Photo by Thomas Kelley on Unsplash

Processed foods filled with chemicals are known endocrine disruptors — hormonally active agents — meaning they cause hormonal imbalances, increase disease risk and prevent your body from maintaining homeostasis.

As well as this, processed foods are linked to overeating — a recent clinical trial published in Cell Metabolism found that when macronutrients are matched, those on a processed diet eat on average 500 calories more when given the chance to snack outside of meals, compared to the group who ate a wholefood diet of the same macros.

Processed foods are also associated with obesity, type 2 diabetes, cardiovascular disease, high LDL cholesterol, mental health illness, neurological decline and all cause mortality. Even when researchers adjust for calorie intake and other confounders like smoking and exercise activity.
['Emilina Lomas']
['Wellness', 'Health', 'Food', 'Diet', 'Weight Loss']