What Causes Obesity – Excess Calories or Excess Carbohydrates?

One of the the biggest (if not THE biggest) points of contention in the health and fitness industries is whether excess calories or excess carbohydrates are responsible for high levels of obesity in the United States.

Calories In/Calories Out proponents: Those in this camp say a calorie is a calorie and that thermodynamics is the driver. That is, if you eat more calories than you expend, you’re going to get fat.

Carbohydrate/Insulin Resistance proponents: Those in this camp generally say that excess carbohydrates are the driver; if you consume too many carbohydrates, especially refined carbohydrates or simple sugars, you will spike your insulin levels promoting insulin resistance and fat storage.

The backstory…

Around 2007 American science writer Gary Taubes made a big splash with his book “Good Calories, Bad Calories.” The book is an extremely comprehensive history of America’s relationship with fat (demonizing it for decades) and carbohydrates (lauding their benefits). In his book Taubes delves into a lot of the anti-fat science to highlight improper use/over generalization of scientific findings. He also contrasts diets from a variety of populations across the world. His conclusion was that the obesity epidemic in the United States is more likely a result of eating too many carbohydrates, not of eating too many calories. In essence, his argument is that quality, not quantity of food, is the driver of obesity.

Taubes recognized that this hypothesis couldn’t be tested without proper scientific studies. Such studies are extremely hard to do well in humans. To date, they just weren’t getting done. Ideally you would need to conduct a double-blinded randomized control trial to prove causality, but even if this couldn’t be conducted, there was much room for improvement. Therefore, Taubes co-founded the Nutrition Science Initiative (NuSI).

I monitored NuSI for several years, but the launch process was slow and I eventually lost track of what they were doing. Recently, I came across a podcast which made me aware that their first major study trying to answer the Calories vs Carbs question was published last year (Hall et al., 2016).

So, what did this particular study look at?

I’m not going to pull out all the details of the study like I normally do, but a brief summary is necessary before I talk about the implications. In the study 17 obese men between 18 and 50 years old were given a baseline diet of fixed calories (~2398) for 28 days and then shifted to a low carb diet (with the same total calories as the baseline diet) for another 28 days. Protein content was the same between diets, so the shift was in replacing carbs with fat, commonly referred to as a ketogenic diet. Both diets contained minimal processed foods or liquid sugars.

But there is a problem in our midst…

A key observation regarding the design of this study is that both the baseline diet and the low-carb diets were likely changes from what the participants had been eating prior to the study. The authors even note that participants may have been eating large quantities of liquid sugar before switching to the baseline diet. Along these lines, the participants may also have been eating more than 2398 calories daily before starting the study. We don’t know for sure because the researchers did not assess diets prior to their study. My reaction to reading this design setup in the paper was, to quote Luke Skywalker in The Last Jedi, “This is not going to go the way you think.”

So, what happened?

Well, just like Luke, I was right. Results indicated that participants on the baseline diet lost about 1lb of body fat over the last 15 days alone. Then, when switched to the low-carb diet, they lost only 0.44lbs of fat over the entire 28-day duration of the diet. Energy balance was also assessed and was found to be negative for both baseline and low-carb diets, with no significant difference between the two.

And, what does this data suggest?

At face value the data suggests that both the baseline diet and low-carb diet result in a negative energy balance, but that the baseline diet was more effective for fat loss. Reducing carbohydrates from the low-carb diet resulted in mostly water loss and minimal fat loss. In essence, the data does not support the hypothesis of the study – that a reduction in carbohydrate will lead to greater fat loss and energy expenditure. Instead, the data seem to show that a calorie is a calorie.

Is that the take-home message?

Not at all. We need to have a preponderance of well-conducted science to feel confident that a phenomenon is true. We’re not there yet. But I’ve highlighted this article as an example of how scientists can paint themselves into a corner if they don’t 1) think about their question carefully and 2) consider all the knowledge available.

Regarding the first point, the authors never had a chance of answering their question properly because they didn’t examine the diet of participants before they started the study. The baseline diet was essentially treatment #1, which was then followed by treatment #2 (the low-carb diet). Was the baseline diet an inadvertent calorie reduction or a carb-reduction diet of its own? Most likely yes. I say this based on my experience as a coach/trainer. I’ve seen time and again that many people who are obese eat excess calories and excess refined carbohydrates/sugar. This leads me into point number two.

If a coach/trainer was involved with the design of this study, they would have wanted to know the start point for each participant because, experience shows, we can get our clients to lose weight by either reducing the total number of calories they eat or reducing carbohydrate intake. Depending on the person and individual situations, both are options that can work. One approach may work best for one person and the other approach for another. This is what experience shows and in fact the science supports this as well – you can find studies in animals and humans that support both sides of the argument.

What does this mean for NuSI?

We don’t know for sure, but it wasn’t good at all. NuSI lost a great deal of their funding when this study was published because investors took the results to mean that Taubes’ carbohydrate hypothesis was wrong. It’s probably not entirely wrong, but needs to be refined much more in light of what we know.

So what should we take away from this?

1) The experience of trainers working firsthand with clients, combined with the scientific studies that exist to date suggest that both calories in/calories out and quantity of refined carbohydrates/sugar can be the driving force for weight gain/obesity.

2) As scientists we often fall into the trap of trying to find a “silver bullet” for problems, but the human body is highly adaptable and seldom dependent on a single factor. Remember, the body strives for homeostasis – equilibrium between interdependent elements.

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