Are All Calories Equal?


Is A Calorie, Just A Calorie?

I am firm believer that when it comes to losing weight and building size and strength, the number of calories you consume on a daily basis, is the deciding factor in whether you successfully meet these goals. But, what about the macronutrients: carbohydrates, fats and proteins? Well, in terms of maintaining and improving general health and performance, I think the ratio of macronutrients in your diet plays a key role in optimising these areas, but in terms of successful pure weight loss and size and strength development, calories in/out is the determining factor.

However, some don’t agree with this and believe that weight loss goes much deeper than just considering the simple calories in/out energy balance principle of ensuring weight loss. Essentially, it is believed that the body doesn’t treat every calorie the same, and thus different macro-divisions between diets (even when these diets all ensure the same calorie intake) produce varying effects in weight loss. Interesting stuff! But what does the science really tell us? And more importantly, is it significant enough for us to start moving away from the simple concept of calories in/out for weight loss?

What Does The Science Tell Us?

At the moment, the research has presented a mix of results on whether diets consisting of different macronutrient ratios of carbohydrates, proteins and fats, actually produce varying effects on weight loss (when total restricted calorie intake is similar). 

A notable study was conducted by Volek et al, 2004 in which they investigated the extent of weight loss, trunk fat mass, resting energy expenditure and body composition in obese men and women which followed either a very-low carbohydrate ketogenic (VLCK) or low-fat  (LF) calorie-restricted diet. Importantly, both diets had participants maintain a calorie deficit of 500 calories per day. So calorie restriction was the same in both diets, thus the only thing that was changed was the macronutrient composition of each diet. With the VLCK diet, the macronutrient ratio was roughly in the range of 9:63:28% (carbohydrate/fat/protein) and the LF diet in the range of 58:22:20% (carbohydrate/fat/protein). 

The results?

At the end of the study, researchers actually found that those (both men and women) which followed the VLCK diet had exhibited greater reductions in trunk fat loss, bodyweight, total fat mass in comparison to those that followed the LF diet. 

The Conclusions?

It seemed like the basic principle of CALORIES IN/OUT were not responsible for the weight loss observed in these participants (since calorie restriction was the same in participants on both diets). So what was the cause of the weight loss? 

One theory is ‘metabolic advantage’ and this might arise due to a range of processes such as increases in protein turnover through gluconeogenesis (breakdown of proteins for glucose production), increased thermogenesis due to increased loss of heat from protein breakdown (protein breakdown is actually inefficient in comparison to carbohydrates). All this sounds plausible, especially given the fact that those who followed the VLCK diets would need to utilise an alternative source of fuel for glucose (energy) production in the presence of very low (or even absent) carbohydrates. The increased protein could serve as this alternative source of energy.

However, as the body is relatively ‘inefficient’ at utilising protein for energy, it’s going to come at a ‘metabolic cost’. But hey, it has to be done, otherwise you die from no energy! This means, using some of the calories that you take in to break it down, of which this breakdown results in the production of heat (thermogenesis). This is actually good news for you because it theoretically means that not all calories you take in, will be utilised by the body as a direct source of energy (known as effective calories). The remaining calories will go in to the thermogenic process of protein breakdown. So in effect, your body is getting even less than you give it, if protein becomes the dominant energy source (as in the VLCK diet). 

A hypothetical situation:

In line with this theory, say you follow a calorie-restricted VLCK diet and your maintenance is 2500 calories. Adopting a -500 calorie deficit, would mean you would need take in 2000 calories each day to lose weight (calories in/out). However, this would not be your effective calories because some of these calories would go to processing the protein as an alternative energy source. So in reality, your effective calories might actually be more like 1800, even lower! Now, say you follow a diet consisting of plenty of carbohydrates, with the same maintenance (2500) and the same daily calorie deficit (-500). Your effective calories would be much closer to 2000 because the body is relatively efficient at processing carbohydrates for fuel in comparison to the protein, so less calories would be needed to break it down. Through this then, it’s possible to see why the VLCK group in the study might have lost MORE weight than those that followed a LF (high carbohydrate diet). 

If every calorie was the same, then we would be assuming that the body could process all macronutrients with the same efficiency, so there would be no ‘metabolic cost’. 

The bottom line: This all sounds great on paper, but the problem is, none of this has actually been tested. This study only hypothesised what might be happening, they did not actually further study this ‘metabolic advantage’. We do know thermogenesis occurs and we know roughly the metabolic cost of producing energy from carbohydrates (~7%), proteins (~27.5%) and fats (~2.5%). But, what we don’t know is if this metabolic advantage was specifically responsible for what was observed in the above experiment. It’s all theory at this point. 

Thermodynamics In Support Of ‘All Calories Not Equal’

An interesting paper was written by Feinman and Fine, 2004 about how thermodynamics can be used to explain why all calories are not equal. According to the authors, the reason why ‘All calories are equal’ has become the guiding principle in weight loss theory, is because it obeys the first law of thermodynamics. Don’t worry, I am not going to get all mathematical! But it does explain nicely why we tend to stick to the whole ‘all calories are equal’ principle to the letter. So what is the first law of thermodynamics?

⇒First law of thermodynamics: Simply states that in an irreversible system, energy cannot be created nor destroyed. It can only be transferred and converted into other forms, but never lost. The total amount of work (governed by work, heat and changes in chemical composition) will always be the same. 

Pretty simple, right? Essentially, this would explain why if you follow two different diets with  the same calorie values (assuming your calorie deficit is the same), you SHOULD lose the same amount of weight regardless of the diet followed. The macronutrient profile for each, shouldn’t make a difference. Why? If calories are the same and the first law holds, then the energy used and transferred in the processing of the macronutrients, should be the same. Thus, both diets of similar caloric values, should produce similar weight losses. However, one thing you might notice is that the first law tells us that the total energy of a system is conserved, and energy can be transferred to other forms (such as heat), but it doesn’t tell us, what the ‘extent of the transfer is’ (e.g. how much energy is transferred to heat). In other words, we have no idea how much energy is transferred to another specific types of energy and so forth. We only know that energy can be transferred in a system. Most of the time, when we talk about diets, weight loss and calories, we are only really concerned with the first law. This is why ‘a calorie is a calorie’ still rules the game.

⇒Second law of thermodynamics: Basically, this relates to the ‘efficiency’ of energy transfer. In other words, when energy is transferred from one form to another, some of it is always dissipated as heat (unrecoverable energy). The more inefficient a system is, the more energy that will be dissipated as heat as it goes through its chemical reactions. The second law also represents entropy. As systems (biological or manmade) undergo a progression to increased disorder, some energy will be lost as heat and some, transferred into other forms during various chemical reactions.

*entropy is a measure of the natural tendency of systems to progress from order, towards increasing disorder. 

In nutrition, efficiency is usually measured through ‘heat losses’ (thermogenesis). Applying the second law of thermodynamics, the ‘efficiency’ in the processing of carbohydrates, fats and proteins through metabolic pathways will be governed by changes in the amount of heat given off during these reactions. The more inefficient these biological reactions, the more heat given off. In line with this, Feinman and Fine, 2004 conducted an analysis of heat given off in response to a diet of macro composition 55:30:15% (carbohydrate/fat/protein) and an intake of 2000 calories. Given the thermic effects of carbohydrates, fats and proteins is 7%, 2.5% and 27.5% respectively, the effective yield of this diet would be calculated as 1848 calories.



However, it was found that when the percentage of carbohydrates in the diet were further lowered, and the remaining calories were equally divided between the fats and proteins, the effective yield dropped further. As carbohydrates were reduced, the body would need to switch to  proteins in order to provide the needed energy for the body. These reactions are ‘metabolically inefficient’ and therefore would require MORE calories from the 2000 calories provided by the diet, in order to break the proteins down. This would correspond with an increase in calories lost as heat and thus a reduction in effective calorie yield (See figure from study below!). This could support a potentially greater degree of weight loss on a 2000 calorie diet as the carbohydrate content was dropped (although not tested here). 

PubMed_Central__Figure_2__Nutr_J__2004__3__9__Published_online_2004_Jul_28__doi_ _10_1186_1475-2891-3-9.jpg 

The conclusion of the study?

According to the study, there is probably more to the weight loss story than simply ‘every calorie is equal’. In fact, given that ‘every calorie is equal’ violates the second law of thermodynamics, there is likely A LOT MORE to the weight loss story! 

Although it’s important to note that none of this can be conclusive to the long-term. 

What happens if you keep reducing carbohydrates so much? 

What happens if you persist in a low-carbohydrate state too long? Will metabolic compensations take place to slow down and even reverse the effects of these metabolic ‘inefficiencies? (Homeostatic mechanisms?) Who knows!

Metabolic inefficiencies obviously do not occur to the same extent in all individuals, what is happening in terms of enzyme or hormonal activity?

Looking at these questions, we just don’t know what the precise link is between metabolic inefficiencies, weight loss and macronutrient changes other than ‘heat lost’. 

However, in light of all this, there was a later study published (over a period of 2 years, so long-term compared to most studies) than the above study. Here, Foster et al, 2010 looked at the extent of weight loss in 307 patients between those that followed a low-fat diet and those that followed a low-carbohydrate diet. They found that at all points during the study, they found no differences in body weight and body composition between the two diet groups. This contrasts with the study by Volek et al, 2004

It’s important to note that the study by Volek et al, was a short-term study, conducted over a period of 50 days, while that of Foster et al, long-term, over 2 years. Although it’s not clear why this happened and no explanation was given, it could be that some kind of metabolic compensatory mechanism was at play over the longer-term to help perturb the benefits from these metabolic inefficiencies. 

The bottom line:

It’s clear that not all calories are the same, as highlighted by the second law of thermodynamics. Metabolic reactions present inefficiencies and these inefficiencies arise as heat given out. While carbohydrates are efficiently processed by the body, protein is the least efficiently processed.

In line with the second law, this would represent as more calories being used in it’s breakdown and lead to more energy given off as heat. In the context of fat loss, low carbohydrate, high protein over other diets of similar calorie content are likely to produce greater levels of weight loss. This however has only been observed in the short-term.

Given that longer-term studies have negated this short-term observation, it’s clear that other mechanisms might be in play that are possibly acting to perturb any effects of these metabolic inefficiencies might have on weight loss in the long-term.

My Recommendation? 

At this time, balancing calories in/out still provides the clear route to successful weight loss. While certain macronutrient ratios might have a positive effect on weight loss, at this time, the research seems to be sparse and non-conclusive. Especially in the long-term.  

Any questions, ask away!


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