A Brief Response to Taubes's Food Reward Critique, and a Little Something Extra

It appears Gary Taubes has completed his series critiquing the food reward hypothesis of obesity (1).  I have to hand it to him, it takes some cojones to critique an entire field of research, particularly when you have no scientific background in it.

The food reward hypothesis of obesity states that the reward and palatability value of food influence body fatness, and excess reward/palatability can promote body fat accumulation.  If we want to test the hypothesis, the most direct way is to find experiments in which 1) the nutritional qualities of the experimental diet groups are kept the same or at least very similar, 2) some aspect of diet reward/palatability differs, and 3) changes in body fat/weight are measured (for example, 2, 3, 4, 5, 6, 7, 8, 9).  In these experiments the hypothesis has both arms and one leg tied behind its back, because the most potent reward factors (energy density, sugar, fat) have nutritional value and therefore experiments that modify these cannot be tightly controlled for nutritional differences.  Yet even with this severe disadvantage, the hypothesis is consistently supported by the scientific evidence.  Taubes repeatedly stated in his series that controlled studies like these have not been conducted, apparently basing this belief on a 22-year-old review paper by Dr. Israel Ramirez and colleagues that does not contain the word 'reward' (10). 

Another way to test the hypothesis is to see if people with higher food reward sensitivity (due to genetics or other factors) tend to gain more fat over time (for example, 11, 12, 13, 14, 15, 16).  In addition, studies that have examined the effect of palatability/reward on food intake in a controlled manner are relevant (17, 18, 19, 20, 21, 22), as are studies that have identified some of the mechanisms by which these effects occur (reviewed in 23).  Even if not all of the studies are perfect, at some point, one has to acknowledge that there are a lot of mutually buttressing lines of evidence here.  It is notable that virtually none of these studies appeared in Taubes's posts, and he appeared largely unaware of them. 
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The Carbohydrate Hypothesis of Obesity: a Critical Examination

Introduction

I'd like to begin by emphasizing that carbohydrate restriction has helped many people lose body fat and improve their metabolic health.  Although it doesn't work for everyone, there is no doubt that carbohydrate restriction causes fat loss in many, perhaps even most obese people.  For a subset of people, the results can be very impressive.  I consider that to be a fact at this point, but that's not what I'll be discussing here. 

What I want to discuss is a hypothesis.  It's the idea, championed by Gary Taubes, that carbohydrate (particularly refined carbohydrate) causes obesity by elevating insulin, thereby causing increased fat storage in fat cells.  To demonstrate that I'm representing this hypothesis accurately, here is a quote from his book Good Calories, Bad Calories:

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