Why are not all calories created equal? A dietitian explains

A calorie is a calorie is a calorie, at least from a thermodynamic point of view. It is defined as the amount of energy needed to raise the temperature of 1 kg of water by 1 degree Celsius (2.2 pounds times 1.8 degrees Fahrenheit).

But when it comes to health and your body’s energy balance, not all calories are equal.

For example, some studies have reported that diets high in protein, low in carbohydrates, or a combination of the two provide greater weight loss than diets with other levels of fat, protein, and carbohydrates.

If every calorie in food was the same, you would not expect to see weight loss differences among people who eat the same number of calories that are distributed in different types of food.

Dietitians like me know that there are many factors that affect what a calorie means to your body. Here’s what we understand about calories and nutrition so far.

Energy actually available to your body

In the late 1800s, chemist WO Atwater and his colleagues devised a system to find out how much energy – that is, how many calories – different foods contain. Basically, he burned up food samples and recorded how much energy they released in the form of heat.

Not all energy in the laboratory that can be burned in the laboratory is actually available to your body. What researchers call metabolizable energy is the difference between the total energy of the food ingested and the energy that passes out of your body, undigested, in feces and urine.

For each of the three macronutrients — proteins, carbohydrates, and fats — Atwood devised a percentage of the calories they contained that could actually be metabolized.

Table showing the available energy for fat, protein and carbohydrates(Buchholz and Schoeller, Am. J. Clin. Nutr., 2004)

According to the Atwater system, one gram of each macronutrient is estimated to provide a certain number of calories. The U.S. Department of Agriculture still uses these calculations today to come up with an official calorie count for each food.

How much energy do you use

What you eat can affect what researchers call your body’s energy consumption. It takes so much energy to keep you alive – energy you use to breathe, digest, keep your blood flowing and so on – along with what you exert to move your body. You may have heard this called metabolism.

Dietary quality can alter the body’s energy consumption, which is also called the thermal effect of food. For example, in one study, people who ate the same number of calories a day, but on either a low-carbohydrate diet or a low-fat diet, had differences in total energy expenditure of about 300 calories a day. Those who ate diets with a very low carbohydrate content used the most energy, while those who ate low-fat diets used the least.

In another study, high-fat diets led to a lower overall energy expenditure than high-carbohydrate diets. Other researchers reported that while replacing carbohydrates with fat did not change energy expenditure, people who increased their protein intake to 30-35 percent of their diet used more energy.

In general, diets high in carbohydrates, fats, or both produce a 4-8 percent increase in energy expenditure, while high-protein meals cause an 11-14 percent increase in resting metabolism. Protein has a higher thermal effect because it is harder for the body to break down. Although these variations are not huge, they can contribute to the obesity epidemic by encouraging a subtle average weight gain.

The quality of the calories you eat

Dietitians are aware of a food’s glycemic index and glycemic load – that is, how fast and how much it will increase your blood sugar level. An increase in blood sugar triggers the release of insulin, which in turn affects energy metabolism and the storage of excess energy such as fat.

Foods like white rice, cakes, cookies and chips are all high on the glycemic index / load. Green vegetables, raw peppers, mushrooms and legumes are all low on the glycemic index / load. There is some evidence that foods lower in the glycemic index / load may be better at keeping blood sugar levels regulated – regardless of the calories they contain.

Reward centers in the brain light up when people eat high glycemic index / load foods, highlighting the pleasurable and addictive effect of foods like candy or white bread.

The fiber content of food is another thing to consider. Your body cannot digest fiber – found in plant foods such as fruits, vegetables, whole grains and beans – for energy. So foods high in fiber tend to have less metabolic energy and can help you feel full on fewer calories.

Empty calories – those from foods with minimal or no nutritional value – are another factor to consider. Things like white sugar, soft drinks and many ultra-processed snacks do not provide much, if any, benefits in terms of protein, vitamins or minerals along with their calories.

The opposite would be nutrient-dense foods that are high in nutrients or fiber while still being relatively low in calories. Examples are spinach, apples and beans.

And do not think of empty calories as neutral. Nutritionists consider them as harmful calories because they can have a negative effect on health.

Foods that are the biggest contributors to weight gain are potato chips, potatoes, sugary drinks and meats, both processed and unprocessed.

On the other hand, foods are inversely associated with weight gain, vegetables, whole grains, fruits, nuts and yogurt.

More for health than calories and weight

It is indisputable that for weight loss, the difference between the number of calories consumed and the number of calories exercised during exercise is the most important factor.

But do not deceive yourself. While weight plays a role in health and longevity, weight loss alone does not equal health.

Yes, some high protein diets seem to promote weight loss at least in the short term. But epidemiologists know that in areas where humans live the longest – close to 100 years on average – they eat a primarily plant-based diet, with very little or no animal protein and low or moderate fat in the form of mono- and polyunsaturated fats.

I often hear friends or clients say things like “It’s the carbs that make me fat” or “I have to go on a low-carb diet.”

But these complaints drive dietitians like me crazy.

Carbohydrates include foods like Coca-Cola and sweets, but also apples and spinach. Cutting down on simple carbohydrates like soft drinks, baked goods with refined flour, pasta and sweets will definitely have a positive impact on health. However, removing carbohydrates like vegetables and fruits will have the opposite effect.

A plant-based diet high in plant-based protein and carbohydrates, mainly from vegetables, fruits, nuts and legumes, is the healthiest diet known to researchers for longevity and prevention of chronic diseases such as heart disease, cancer, hypertension and many other conditions.

The modern western diet suffers from an increase in the amount of calories consumed with a concomitant decrease in the quality of calories consumed.

And researchers now know that calories from different foods have different effects on fullness, insulin response, the process of converting carbohydrates into body fat and metabolic energy consumption.

In terms of your health, count more on the quality of the calories you consume than the calorie count. The conversation

Terezie Tolar-Peterson, Associate Professor of Food Science, Nutrition and Health Promotion, Mississippi State University.

This article is republished from The Conversation under a Creative Commons license. Read the original article.


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