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Our Brains Like Sugar More Than Fat



sharma-obesity-brainFat, sugar and salt are often put up as the holy trinity of unhealthy eating. Together, foods considered high in one or more of these substances are generally considered “highly palatable” – a fancy way of saying they taste good.

However, biochemically, biologically, physiologically, and otherwise, these substances are vastly different (NaCl or salt being the most simple of the three).

Now, based on a fascinating neuroimaging study by Eric Stice and colleagues, from the Oregon Research Institute, published in the American Journal of Clinical Nutrition, suggests that sugar and fat act very differently on the reward areas of the brain (salt was not studied).

Highly sophisticated functional magnetic resonance studies were conducted in 106 non-obese adolescents who were given equicaloric amounts of high-fat/high-sugar, high-fat/low-sugar, low-fat/high-sugar, and low-fat/low-sugar chocolate milkshakes with a tasteless solution acting as control.

While high-fat shakes resulted in greater activation in brain regions involved in associative learning processes (caudate and hippocampus) and somatosensory regions (postcentral gyrus), the high-sugar shekes prompted greater activation in regions associated with reward and motivation (insula and putamen), oral somatosensation (Rolandic operculum), and gustatory stimulation (thalamus).

While increasing sugar in low-fat milkshakes caused greater activation in the bilateral insula and Rolandic operculum, increasing fat content did not elicit greater activation in any region.

The authors offer the following explanation for these interesting findings:

“It is possible that this pattern of findings emerged because sweet is a primary reward, and it has been subsequently theorized that humans are predisposed with a sweet preference, whereas fat is viewed as a texture, and preferences are acquired through conditioning at an early age.

It is also conceivable that gustatory regions that encode tastes project more directly to reward-valuation regions than oral somatosensory regions that encode viscosity and, therefore, the fat content of foods. Collectively, results from the current study supported the notion that increasing the sugar content of food results in a greater neural response than increasing the fat content.”

From a practical perspective, this study clearly implies that while it may be easy to make low-fat foods more palatable and rewarding by simply adding sugar (something that we know happened as a result of the “low-fat” diet craze), it is far less likely that adding fat to low-sugar foods (and beverages) would do the same.

Thus, the authors suggest that,

“…policy, prevention, and treatment interventions should prioritize reductions in sugar intake.”

Given the direct stimulatory effect of sugar on reward centres, I can only wonder how cutting sugar will affect reward seeking behaviours, which makes me wonder if any of my readers have ever experienced increased cravings for other “stimulants” when they have tried to cut down on sweets.

@DrSharma
Gurgaon, India

Hat tip to Danielle Aldous for alerting me to this paper.

ResearchBlogging.orgStice E, Burger KS, & Yokum S (2013). Relative ability of fat and sugar tastes to activate reward, gustatory, and somatosensory regions. The American journal of clinical nutrition, 98 (6), 1377-84 PMID: 24132980

 

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17 Comments

  1. What I find when I cut down on sugar, I look for it in simple carbohydrates. My sneaky mind looks everywhere it can for sweets.

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  2. I have cut out sugar completely and have not been eating it for a little more than one year. The longer I go like this the less I want sweet food. Berries is the most sweet I eat and even that at time feels overly sweet. Today I had an apple but didn’t finish it because I simply don’t like the taste of them anymore.

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  3. I get cravings for sweets occasionally but artificial sweeteners gets rid of the craving very effectively. The inventors of aspartame and sucralose each deserve a Nobel prize.

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  4. Having quit smoking over 8 years ago and considering myself at “termination” I was quite shocked to find that every now and then a craving for a cigarette will still hit me like a wave. It is a fleeting but intense almost physical reaction and lasts for no more than a few seconds. Not suprisingly, these “waves” usually correlate when I am trying to deny myself something else, like an entire jumbo pack of skittles! Not giving in to either behaviour – there’s the rub…

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  5. Interesting findings to be sure. That humans express a somewhat greater preference for the taste of sugar over fat maybe isn’t that surprising. But in evolutionary terms, one would think that our bodies might have placed a greater premium on ingesting lipids versus sugary carbohydrates, given the higher energy-density of fat, so the results definitely cast doubt on that idea.

    I would be interested to see if sugar substitutes like stevia produce the same effects in the various reward centres of the brain as genuine sugars. Adding in natural sugar replacements might be a way to increase the palatability of low-fat foods without boosting calories as happened in the earlier low-fat craze.

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  6. My own experience:

    Refined carbs and sugary foods make me hungrier. They are, as the saying goes, very “more-ish”. I enjoy these foods, but I have learned I can never get enough of them. The more I eat, the more I want.

    If I go overboard and indulge myself in a yummy food binge (high carb, high sugar) I know I have to go a few days eating only low carb food (vegs and meat and fish) until the craving for sweet treats goes away. I have to tell myself I’m not really hungry, I’m just having leftover cravings caused by my sugary high carb excess.

    If I eat a meal very high in fat (like a bacon/sausage/fried egg/home fries breakfast at a diner), I am not hungry for more.

    Neither of those types of foods are healthy.
    But I know I can have the “bad” breakfast, and I won’t want more and more. (I eat that about once a year)
    And I know if I eat the sugary high carb treats I’ll be hungry for days, I’m very likely to go totally off a healthy routine, gain weight, and have to go through a “detox” week of being hungry while eating good but lowcarb food, before I can be satisfied eating an ordinary healthy diet.

    The result of this is that, for me, it is better to avoid high carb sugary food completely – it’s not worth having at all, because there’s no point in starting a craving binge.

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  7. On another topic …
    Dr Sharma, would you have any comment on the article
    “There’s no such thing as healthy obesity, new findings show”
    by Adrianna Barton, Globe and Mail, Tues Dec 3, 2013.

    She reports on research by:
    Dr Zinman, Mount Sinai Hospital Lunenfeld-Tanenbbaum Research Institute, Toronto

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  8. As an exobese, I will say that sugar is the most evil substance created by man, followed closely by all processed carbohydrates. These increase hunger and salt is the primer for uptake of glucose and fructose in the gut.

    Sugar and finely ground carbohydrates do not belong in the human food supply for anyone who has weight issues. But what do I know?

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  9. Unfortunately the conclusion that “our brains like sugar more than fat” cannot be drawn from this study. The reason is that the study only looked at short-term fMRI responses to fat and sugar ingestion. The difference may simply be due to the kinetics of sugar vs. fat detection by the senses and brain.

    Fat is “habit-forming” and drives food-seeking behavior quite readily in animals and humans, just like sugar does. I don’t think this study supersedes data that actually examine the rewarding properties of these substances using behavioral measures in animals and humans. Reward, ultimately, is defined by behavior not brain activity.

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  10. I’ve been eating low carb high fat for the last year. Cognitively it has been wonderful. I couldn’t think if I was hungry, and I was hungry often. I also found that i thought much better if I consumed saturated fat. So I was resigned to just being overweight. (My profession requires a sharp mind.) After eating low carb high fat not only have I lost 35lb but my cognitive abilities have increased. I also do fine when I haven’t eaten in a while. It’s been awesome.

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  11. This makes sense when you look at breastfeeding. At the beginning of any breastfeed, the milk is higher in lactose and lower in fat than the milk at the end of the feed. It’s called “foremilk”. Given the neural response to sugar, this would encourage the baby to keep on nursing, getting protein for the heart and muscles and lungs, sugar for the brain and cells, water for hydration. Then as those needs are met the milk switches to higher fat content — “hindmilk” — hydrated, and no longer as rewarded by the high fat hindmilk, the baby is contented to end the feed. If fat content was high throughout the feed the baby might not be as motivated to feed long enough and even if he was getting adequate calories he would risk dehydration.

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  12. Is is the sweetness or the sucrose that is the problem?

    Every time I see proposals to regulate/ban/tax sugar, I wonder if it will only move the problem (onto non-nutritive sweeteners) or even make problems worse. Some studies, though not all, seem to indicate that replacing sucrose by calorie-free sweetness increases the risk of obesity and diabetes. In this particular study, if I understand correctly, they show that sweetness, not sugar, excites the brain, is that correct?

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  13. I have a friend who is a recovering alcoholic. He recently mentioned to me how he noticed his intake of pop and candies has dramatically increased since he stopped drinking alcohol.

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  14. I have an enormous sweet/starch tooth, and the only thing that has helped reduce the cravings is to eat more protein, especially beef, chicken and tofu. Fish, not so much, and I don’t eat pork at all because I don’t like the saltiness of most salt-cured pork products. Vegetables and fruits seem neutral to me — they don’t fill me up, and they’re not particularly satisfying. I wonder if it has something to do with the Krebs cycle, which I admit to not understanding very well.

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  15. I became addicted to sugar at a young age. I believe that is my primary source of reward and that once I’ve satisfied my sugar craving, I feel functional. The trick I use to avoid weight gain is to eat oatmeal throughout the day. I make it into pancakes with different recipes and always have a batch in the fridge.

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  16. I guess that we see that with our patients a lot as they always comment that the most difficult of 3evils to control is the sugar
    We know how sugar controls Insulin secretion and increased Insulin in turn plays around
    with hunger -satiety control mechanisms still what we read today tell us more specifically how sugar activates reward centers more intensely resulting in more loss of control or binge eating trends
    Understanding mechanisms is key to professionals working w Obesity as much as its important for those suffering

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