No, Walnuts Aren't the Key to Weight Loss
Walnuts already have an image as a healthyish food, but the California Walnut Commission wanted to know more. A new study asked if walnuts-already associated with lower risks of heart disease and Type 2 diabetes-might deliver some of their health benefits by changing our brains' reactions to food.
The Story: First of all, this study tested absolutely nothing about weight loss. It's also worth noting up front that it was partly funded by the California Walnut Commission, but the CWC had nothing to do with the design, execution, or publication of the research; the researchers came up with the study themselves and applied to the CWC for funding.
So if this wasn't about weight loss, what was it about?
This was a small but tight study-double-blind and placebo-controlled. Nine obese participants were given either a walnut shake or a placebo (walnut-flavored and identical in calories and macronutrient breakdown) as part of their weight-maintenance diet for five days. This was repeated twice, with a month cool-down between, with those who got the placebo in round one given walnuts in round two and vice versa. At the end of the five days, subjects were asked about their hunger levels, and their brains' reactions to images of food were recorded in an MRI.
In the surveys, walnut-drinkers reported feeling less hungry than the placebo group (matching previous findings from this research lab). The brain scan results were the new part, revealing that when shown images of high-reward food (compared to low-reward food like vegetables, or non-food like rocks), walnut-drinkers showed more activity in an area of the brain called the insula, which is thought to be involved in appetite and impulse control. This functional MRI analysis, or fMRI, offers researchers exciting insights into brain activity, but flaws have been found in its complex methodology, and the interpretation of fMRI findings is still controversial.
Does that activity mean that walnuts give you more will power when faced with junk food? Not necessarily. Would these results apply in lean patients, beyond the obese test subjects? No clue. Are walnuts special or would other nuts work? Idk.
Okay, but how did walnuts have an effect on these participants' brains? I would love to know, as would the researchers behind this study. This is a baby step in the long march toward figuring out the mechanisms behind-and extent of-the apparent health benefits of one of the many, many foods that people eat.
The Takeaway: Walnuts might help you feel more satisfied, and they might stimulate a part of your brain that might boost your impulse control. We can draw our own conclusions about how satiety and impulse control affect our ability to eat less, but this study says absolutely bupkis about weight loss.