Why a Calorie Isn’t Just a Calorie
Sunday, August 2, 2015
LifeTime WeightLoss in Metabolism, Nutrition, Paul Kriegler, Thermic Effect, calorie math, calories, gut bacteria, gut health, macronutrients, metabolism, microbiota

Fat, carb, protein - does it really matter what form a calorie comes in? 

In the tidy little illusion of calorie math, no. We treat calories like currency – all totals being equal whether counted in coins, bills, or silver bars.

Yet, is a calorie really a calorie, no matter the form or source? Under all conditions to all individuals at all times?

We tend to think this way. Yet, the science begs to differ. 

Technically speaking, a calorie is a measure of how much energy something releases when it’s combusted in a closed system (called a bomb calorimeter in laboratory settings). 

One calorie is the amount of energy required to raise the temperature of one gram of water by one degree Celsius. The calories reported on food labels are actually kilocalories, often written with a capitalized “C.” (That’s why you’ll see me capitalize references to Calories for the rest of our discussion (or list them as kcal).

But the real question is this: what does the calorie question mean for your healthy eating? Let’s break it down.

Numbers Sometimes Lie: Questionable Calorie Counts

I hate to break it to you, but the calorie counts we’ve been conditioned to depend on over the last 50 years or so are flawed. This fact alone might explain a lot to those who have struggled with weight despite scrupulous “calorie counting.”

The USDA maintains one of the most extensive, free food databases in the world. The scientists who perform the lab analyses to determine the Calorie content of foods recommend the public treat these numbers as estimates at best. The numbers reported are not exact measures, mostly because they are tested in a closed system, where energy cannot be created or destroyed. 

Contrarily, our bodies are actually open biological systems, so the principles of exact Calorie counts are already partially flawed based on the open versus closed system concept of energy. Go figure. 

To add a food item to the database, a food manufacturer can either perform its own bomb calorimeter testing (costly and time-consuming) or use existing ingredient data from the USDA database to extrapolate the data to their product (quick and dirty method). To control costs and maximize profits, which method would you follow?

When reporting final Calorie counts for labels, these values need to be accurate within 20% of actual measures, but in all reality no one really checks this before a product reaches our shelves. Perhaps that’s why when researchers do investigate commercially prepared foods, the calorie accuracy is all over the map. Thus, a more truthful name for 100-calorie packs could be “somewhere around 80- to 120-Calorie packs – we think.”

To muddy the waters a bit more, many free calorie-counter apps source their data from the huge USDA database and allow their millions of users to also create custom foods for all other users to select from. This explains why there may be upwards of 30 choices for chicken breast when you go to log your food. Your Calorie counts are only as accurate as Joe-user’s interpretation or best guess. Whoops!

Of course, being aware of what you’re eating and how much you’re eating can be helpful for changing nutrition behaviors. In fact, I think at certain points in one’s weight loss or body comp change process, it’s vital to keep a food diary of some sort to raise awareness (e.g. written, app-based, or photo records). 

Sadly, even if you have the best intentions by trying to track your Calories accurately, your 1500-Calorie plan could really be supplying anywhere from 1200 to 1800 Calories! Manipulating your food choices based solely on Calories isn’t really the best idea anyway. Let me explain.

Thermic Effect and Hunger Suppression: Different Calorie Sources Produce Different Outcomes.

Fun fact: when you eat different foods, your body actually expends different amounts of energy digesting, absorbing, and metabolizing the nutrients. It’s called the thermic effect of food. Similarly, the macronutrients (e.g. carbs, fats, proteins, and alcohol) also trigger different hormonal responses. A Calorie is not just a Calorie once we eat it. 

Of the main food sources (excluding alcohol), protein-rich foods have the greatest thermic effect (PDF), and they seem to suppress hunger better than any other macronutrient. A whopping 25-30% of the Calories in the protein you consume are spent just digesting it

This means a 100 kcal portion of protein (3-4 oz) will only net about 75 to 80 kcals for your body. Even better, protein tends to trigger the most helpful hunger-managing hormones, which increases satiety.  

Contrast the high thermic effect of protein with that of carbohydrates (6-8%) and fats (0-3%), and it seems that eating protein with every meal should be a main focus of everyone who wants to stimulate metabolism and manage hunger at the same time. 

Perhaps most shocking to me is the fact that certain types of carbohydrates – namely simple sugars (e.g. glucose, fructose) and refined grains are particularly stealthy at eluding our sense of fullness. They have low thermic effect and are low in fiber, which decreases their thermic effect even further compared to high-fiber carbs like veggies, fruit, or whole grains. 

In fact, researchers found whole, unprocessed meals demand nearly 50% more energy to digest and absorb compared to processed meals containing the same amount of calories! Not surprisingly, the higher thermic effect meal also appeared to significantly improve satiety measures (fullness). (PDF)

Fructose, in particular, is likely the worst source of calories for us to consume. This now-abundant, super sweet, super cheap form of added sugar is known to follow much different metabolic pathways than other carbohydrates, induce altered nervous system signaling, and bypass hunger hormone responses. The amount of fructose we now consume even seems to be a main driver of the development of insulin resistance - and its progression to diabetes.

The bottom line is this: to keep your metabolism humming, your hunger managed, and fat storage averted, eat plenty of fibrous vegetables, ample protein, and wholesome sources of starchy carbs according to activity level. And, of course, minimize your intake of processed grains and added sugars. 

Yet, emerging evidence suggests we can’t stop there either. Even beyond the thermic effect, there’s more to this metabolic picture. 

You’re Not What You Eat - but What You Eat, Digest, and Absorb.

Most people I know eat food, not Calories. They digest proteins, carbohydrates, and fats, not Calories. They absorb nutrients and metabolize energy, not Calories. The amount of energy absorbed and metabolized can be expressed as Calories, but that’s not what we eat, digest, and absorb.

What you absorb and what your gut microflora absorbs (the bacteria living in your digestive tract) can determine a lot about your weight. 

Researchers have shown marked difference in bacterial profiles of normal weight and obese humans and mice. (PDF)

In fact, the different types and balance of bacteria living in our colons seem to have a profound effect on how many Calories we extract from our food, rendering Calorie counting all but useless unless you know which bacterial pattern you have.

Additionally, the types of bacteria living in the gut may also play a role in preventing metabolic syndrome and diabetes. It appears our genes have a role in determining which strains of bacteria thrive and which struggle in our individual systems, but our food environment also plays a role. Even those with ideal bacterial balance may be subject to harmful bacterial balance shifts if exposed to high enough doses of artificial sweeteners.

We may think we know plenty about the Calories contained in our food choices and even understand a great deal of how our bodies metabolize various foods, but we’re just beginning to learn how our gut microflora influence our entire biochemical relationship with what we eat. 

In the end, there’s quite enough evidence to support the argument that all Calories are not created equally. In fact, there’s plenty of evidence to suggest not counting calories as a primary focal point in your health pursuits. Instead, turn your attention to the quality of foods you consistently choose, and the rest (and results) will usually regulate themselves!

Thanks for reading. Are you interested in learning more about how the caloric-metabolic picture works for your health and weight loss? Talk with a dietitian today. 

In health, Paul Kriegler - Corporate Registered Dietitian

This article is not intended for the treatment or prevention of disease, nor as a substitute for medical treatment, nor as an alternative to medical advice. Use of recommendations in this and other articles is at the choice and risk of the reader.

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