So . . . IS a calorie a calorie or not?

Let’s take a look at the latest published study regarding the effects of 3 different eating plans on maintenance of weight loss.

Study Details

Twenty one overweight and obese, but otherwise healthy, adults first went through a weight loss phase, all of them losing 10-15% of their initial weight.  This was followed by a 4 week standard maintenance plan, the same for all participants.

The study then had each individual follow three different diets for one month each (in random order), with followup to keep calorie levels appropriate for maintenance.

Researchers found that those on a low carb plan (10% carb, 60% fat, 30% protein) maintained weight  eating more calories than those on a low glycemic index diet (40% carb, 40% fat, 20% protein) or a low fat diet (60% carb, 20% fat, 20% protein).  The difference was statistically significant, with about a 300 calorie difference in total calories burned between the very low carb diet and the low fat diet.  The low glycemic index diet resulted in maintenance metabolism values between the other two.

What does this mean for you?

1.  Does this mean that a calorie is not a calorie, that in fact it depends on where it comes from?

2.  Does this mean that everyone wanting to maintain weight loss should follow a very low carb plan?

Question #1:  Is a calorie a calorie?

I don’t think the answer is a simple “yes” or “no”.  Regardless of the blend of macronutrients (carbs, fats, and proteins), a calorie of any food is the same.  In that sense, “a calorie is a calorie”, which is just a unit of energy.

What happens to the calories in food after eating is less clear and more controversial.  Energy conservation dictates that available calories must either be burned or stored; they cannot just disappear from food.  The extreme complexity of how metabolism works has created confusion among dieters and research scientists alike.

We would all like to know:  Does the rate we burn calories – metabolism – speed up when certain diets are followed?  If so, this would mean that, while a calorie is technically a calorie, the food source actually affects metabolism.  While this study’s results suggest that this may be true, previous studies are not all in agreement.  We simply do not know the answer to this question yet.

The study authors agree that the time frame was short, and longer studies are needed.  Close supervision and expensive lab testing provided detailed biochemical data, but also made it difficult to include large numbers of participants.  This is another drawback of the study.

Note:  Whether or not the source of calories matters from a metabolic standpoint (how much we burn) or not, I believe that food choices significantly affect the number of calories most of us consume.  It makes sense that eating food that is nourishing and hunger-satisfying will allow a person to consume fewer calories than eating lots of calorie-dense low quality food.  This may prove to be even more significant than how foods metabolize in the body, at least for some people.

Question #2:   Should everyone wanting to maintain weight loss follow a very low carb plan?

This question gets to the core of my personal beliefs on the topic of weight loss and maintenance.  Studies look at groups.  They provide valuable information in that context, but you are an individual.  A study may give you the piece of information that unlocks the secrets of your personal weight loss and maintenance puzzle, or you may be one of the people for whom it is not the best answer.

Let me make my point by looking at this particular study.

There were only 21 participants who completed the study.  That is not a large sample size.  I am not saying that the study was poorly designed, or that the results are not statistically significant.  The design seems sound, and the results are significant for the group as a whole.

Within a sampling of 21 people, even a small number who do not conform to the group finding could be an indicator of important – and personally significant -variation among group members in terms of macronutrient metabolism.

Looking at the graph depicting each individual’s metabolism on each of the 3 maintenance diet regimens (Figure 3 of the study), there is quite a lot of variation among individuals, although researchers correctly reported significant differences among the 3 diets overall – based on the statistical mean values of the group.

Consider that at least 6 of the participants burned more or approximately the same amount (within about 100 calories), on the low fat diet when compared with the very low carb diet.  Furthermore, the trend of increasing metabolism with decreasing carb content – again, significant for the group, with the group metabolism being lowest on the low fat diet, intermediate on the low glycemic index diet, and highest on the very low carb diet – did not hold for at least 11 of the participants.

Bottom line:  Whether or not a very low carb plan will help you maintain weight loss best is still not clear based on the research.

Please note:  Due to difficulty in reading all of the data points, for the purposes of this discussion I only included data for the 16 participants whose graphs could be clearly followed in Figure 3.  I was not able to get numerical data corresponding to data points from the researchers, since they are still performing further analysis.  

What about the human factor?

Looking at scientific studies can be confusing enough, but trying to find the right plan for you is further complicated by what I call the “human factor.”  Because this was a controlled study, participants did not get to choose their food. In the real world, not only is it likely that one plan will not biologically fit all,  human beings do not consume calories like a machine might, or even like a pet would if meals are carefully controlled.

Most of us freely choose food, and choices can be highly emotionally driven at times.  Even if you find the best plan to satisfy your physical hunger needs on the fewest number of calories – the goal, I believe – there is still a significant human component.  This is what I see people struggling with most.

I see people who overeat certain foods because there appears to be something affecting their self control in a chemical way.  Something about the food – probably salt, fat, sugar or some combination – feels “addictive”, whether or not it technically fits the definition or not.

I also see people who overeat because their dieting mentality is setting them up for bingeing.  In this case, beliefs – that certain foods are off limits, that pleasure in general is bad, or that they should be able to keep going on a measly amount of food – get in the way of more moderate thinking and eating.  Control is lost when even a small misstep occurs, because they have “blown it” already.  Unrealistic expectations are to blame.

These human factors cannot be omitted from a realistic approach to a weight loss or maintenance plan.  Even though it is useful to know that a study found a very low carb plan the best for maintaining metabolism for a group of 21 people, the authors make the point – so obvious to me from my nutrition counseling – that very low carb plans just are not easy for most people to follow long term.  Compliance is the most important requirement for success with any plan.

The researchers make this point as well.  They conclude that, “Ultimately, successful weight-loss maintenance will require behavioral and environmental interventions to facilitate long-term dietary adherence.”


Results of past studies have not all agreed with this study’s findings.  More research is needed to help clarify if indeed there are significant differences in the metabolic effects of different macronutrients.  I believe it is unlikely that there is one perfect blend of nutrients for everyone.

Maybe a reduced carb plan – either very low or moderately low – will work well for you, but it is important to balance the scientific knowledge with real life and realistic expectations.  Otherwise, the plan is just another unrealistic expectation that sets up a feeling of failure.

One of the keys is to figure out the combination of foods that works best for you to balance hunger control with taste preferences and healthy management of emotional life.  This is not as simple as percentages of carb, fat, and protein.


For a list of the glycemic index and glycemic load of many common foods, click here.  The three study diets mentioned above represent glycemic load values that were low (very low carb diet), moderate (low glycemic index diet), and high (low fat diet).  For general information about glycemic index, read my past post on the subject.  Glycemic load is a better indicator of the total amount of carbohydrate entering the body, and the overall blood sugar effect of a person’s diet, than glycemic index.

4 thoughts on “So . . . IS a calorie a calorie or not?

  • Thank you for providing a fair review of this study. We need objective, balanced information like this to sort through the myriad of “News” snippets about diet and weight loss flooding our environment!

  • Thank you for sharing this study and for also reminding me that I need to look at the human factor of my eating plan so I can actually life long healthy improvements not momentary fleeting successes.

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