Variable response is not the same as no response

I saw this going viral:

I have seen many people interpret this study to mean there is no response and thus not addictive. But the study showed that n=29 participants out of n=50 did see a response, albeit a small one, as shown in green below. But this is not the same as no response. This can account for how some people still become addicted and overeat and subsequently become obese. It’s just not the main driver of obesity.

The study went viral in part because people want to believe that food is not addictive or has stimulative properties, yet at the same time overeating causes obesity. In an ideal world, people eat for energy in the form of macronutrients, and go about their day. But it’s not that simple. How does this simplified explanation explain why obese people tend to choose rich, calorie-dense foods. If food was solely for energy and not stimulation–or if energy and stimulation were unrelated–then why would anyone buy junk food at all and risk obesity and other possible negative side effects?

From the intro: “Instead, we found that postingestive striatal dopamine responses were highly variable, not statistically significant, and not significantly related to adiposity.” Either he didn’t read the study, which in the title says it’s variable, or read it and misinterpreted the results. Either way, it does not give me much confidence in his advice or that possessing a doctorate is a signifier of high intelligence or expertise.

From the study, “Distribution of percent change between fasting D2BPralco and D2BPralco after consumption of milkshake, with individuals displaying dopamine release (green, left, “Responders”, n=29) and those who did not (purple, right, “Non-responders”, n=21).”

Individual variability of dopamine response is expected of addictive substances. Not everyone who smokes cigarettes becomes addicted or gets an effect from the nicotine, but enough do that it’s a multi-billion-dollar business. The vast majority of people who use hard drugs do not become addicted. Given the popularity of junk food, evidently a lot of people do get a response, just not all of them.

Thus, postingestive striatal dopamine responses to an ultra-processed milkshake were likely substantially smaller than many addictive drugs and below the limits of detection using standard PET methods.

This is expected and counterintuitively is ideal for inducing a long-term addiction. Cigarettes for example are equally or possibly even more addictive than elicit drugs despite being much more mild. It’s not so much that nicotine is more addictive than cocaine, but that smoking is a much faster and effective delivery method to the brain than injecting or snorting the substance. The mild response means the body is not overwhelmed and thus craves more of the substance over a longer duration, which is what you want when maximizing sales and creating a loyal customer to the product. Second, fewer adverse side effects in the short-term, like overdosing, even if smoking kills in the long-run.

Junk food ‘works’ precisely because it does not overwhelm, but rather the insulin spike provides enough of a kick or buzz to keep the person craving more later. Artificial sweeteners like sucralose are much stronger than sugar, but does not work as well as the classic ‘fat and sugar’ combination found in junk food, which is why cane sugar or butter alone are unpalatable, but peanut butter cups are great. This is what the ‘bliss point’ is about, in which many variables like sweetness and texture are optimized, but no single variable is maximized.