The last two posts on fat and carbohydrate were written to answer a few important, but relatively narrow, questions that I feel are particularly pertinent at the moment:
Was the US obesity epidemic caused by an increase in calorie intake?
Could it have been caused by an increase in carbohydrate intake, independent of the increase in calorie intake?
Does an unrestricted high-carbohydrate diet lead to a higher calorie intake and body fatness than an unrestricted high-fat diet, or vice versa?
Could the US government's advice to eat a low-fat diet have caused the obesity epidemic by causing a dietary shift toward carbohydrate?
However, those posts left a few loose ends that I'd like to tie up in this post. Here, I'll lay out my opinions on the relationship between macronutrient intake and obesity in more detail. I'll give my opinions on the following questions:
What dietary macronutrient composition is the least likely to cause obesity over a lifetime?
What dietary macronutrient composition is best for a person who is already overweight or obese?
I frequently encounter the argument that obesity research has failed because it hasn't stopped the global increase in obesity rates. According to this argument, we need to re-think our approach to obesity research because the current approach just isn't working.
Grant funding for obesity research keeps increasing in the US, and the prevalence of obesity also keeps increasing*. What gives? Maybe if we just scrapped the whole endeavor we'd be better off.
Let's take a closer look at this argument and see how it holds up.
Why Do Research?
There are two fundamental reasons why we do research:
To gather accurate information about the natural world. This information is intrinsically valuable because we like knowing how the world works, and it may eventually have practical value that's not immediately obvious.
Practical applications. We want to solve problems and improve our lives.
If we want to determine whether or not obesity research has failed, we should evaluate it using those two metrics.
Has Obesity Research Gathered Accurate Information?
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One valid objection that came up in the comments is that calorie-controlled diets in a research setting may not reflect what happens in real life. For example, in a context where calorie intake isn't tightly controlled, diet composition can impact calorie intake, in turn affecting body fatness. This, of course, is true, and it forms one of the central pillars of our fat loss program the Ideal Weight Program.
Some low-carbohydrate diet advocates argue that the obesity epidemic was caused by US dietary guidelines that emphasize a carbohydrate-rich diet*. The idea here is that the increase in calorie intake was due to the diet shifting in a more carbohydrate-heavy direction. In other words, they're hypothesizing that a carbohydrate-rich eating style increases food intake, which increases body fatness**. According to this hypothesis, if we had received advice to eat a fat-rich diet instead, we wouldn't be in the midst of an obesity epidemic.
Fortunately for us, this hypothesis has been tested-- many times! Which eating style leads to higher calorie intake and body fatness when calories aren't controlled: a carbohydrate-rich diet, or a fat-rich diet?