A New Study Explains Why Carbs and Fat Together are Irresistible

A study that is due to be published on July 3, 2018 in the scientific journal Cell Metabolism is the first to demonstrate that compared to foods high in carbs or fat, foods with both carbs and fats together result in much more dopamine being released from the striatum, which is the reward-center of our brain [1]. Dopamine is the same neurotransmitter that is released during sex and that is involved in the addictive “runner’s high” familiar to athletes. This is one powerful neurotransmitter!

It is thought that there are separate areas of the brain that evaluate carb-based foods and fat-based foods and both are involved in the release of dopamine, but when carbs and fat appear in the same food together, this results in what the researchers called a “supra-additive effect“. That is, both areas of the brain get activated at the same time, resulting in much more dopamine being released and a much bigger feeling of “reward” being produced.

This combination of carbs and fat in the same food is why we find foods such as French fries, donuts and potato chips irresistible.

In fact, the study found that people were willing to pay more for foods that combine both carbs and fat than for foods that were only high in carbs but not fat such as candy, or only high in fat but not carbs, such as cheese.

This powerful reward-system involving dopamine is why we will choose the fries over the baked potato and why we have no difficulty wolfing back a few donuts, even when we’ve just eaten a meal.

This “supra-additive effect” on the pleasure center of our brain, along with the fact that more insulin is released when both carbs and fat are eaten together[2] may help explain the roots of the current obesity epidemic and the metabolic diseases such as Type 2 Diabetes that go along with it.

Carbohydrate intake was high in the early 1900s and gradually decreased until about 1954, leveled off, then began to increase again[3]. What caused that to occur? At that time, ultra-refined carbohydrates began appearing in the market and these by their very nature were devoid of the whole, unprocessed grain that slows the release of insulin [3]. Excess release of insulin triggered by the constant eating of ultra-refined carbohydrate foods underlies the process of how insulin resistance develops and in time, how Type 2 Diabetes develops [3].

The early 1950’s was also when the “diet-heart hypothesis” proposed by Ancel Keys took root, along with the recommendation that Americans (and later, Canadians) reduce their consumption of saturated fat (more in this article).  With the recommendation to decrease saturated fat was the necessity to create fats to replace them, which is when and why both soybean oil and later, canola oil were created (see this article for more information). These industrial seed oils began to replace natural fats such as butter, lard and tallow in home and restaurant cooking, frying and baking.

With the creation of "polyunsaturated vegetable oils", French fries were now a healthy food - after all, they were vegetables fried in "healthy polyunsaturated fat". 

What could possibly go wrong?

This new study provides the missing link as to the mechanism by which the “perfect storm” was created. That “perfect storm” was the simultaneous appearance in the late 1950s and early 1960s of ultra-refined carbohydrates and industrial seed oils (promoted as “heart healthy” by the American and Canadian Dietary Guidelines) that literally hijacked the reward system of our brain!

Is there little wonder why rates of overweight and obesity began rising at in the early 1960s and have continued to rise dramatically ever since?

As far as our brains are concerned, French fries are much more desirable than a baked potato and donuts and pastry much more desirable than toast because they literally make us feel good!  Eating French fries and pastry results in considerably more dopamine being released than eating baked potato or plain toast. Eating these foods produce something comparable to a “runner’s high” in people that have never run a block or have even gotten off the couch!

While discovery of the dopamine-centered mechanism is new to this study, the food industry has known for some time that processed foods containing both carbohydrate and fat will result in people coming back and buying more and more of their product. Carbs and fat is why Pringles® chips could boast “betcha can’t eat just one!“, but it’s not just Pringles®. This combination of carbs and fat is in all processed foods; from so-called “junk food” such as chips and Cheezies® to foods that are perceived as “healthy foods”, such as granola bars and commercial peanut butter.

Carbs and fats together are the essence of “fast food” – from Big Macs® dripping with cheese and mayo sandwiched between several buns, to French fries of all types, super-sized or not.  People may joke about “junk food being addictive”, however understanding the “supra-additive” effect of carbohydrate combined with fat makes these foods as addictive to our brains as a “runner’s high” is to an athlete, or what makes people seek out sex. Addictive? Maybe not in the truest sense of the word except in cases of food addiction, but certainly in the rest of us there is a powerful draw to want to eat them.

Knowing and understanding this mechanism is of no small consequence! It should inform our food choices.

We need to be aware of foods that we eat that “hijack” our appetites. They could be “healthy foods” like cashews that are both high in fat and high in carbohydrate.  Given what we know about the triggering of the reward system in the brain, should those of us with current or past weight problems have them around?

Another way this knowledge should inform our food choices is around the concept of “cheat days”.  People who see me seeking weight loss often ask me about whether they can have one day a week, or one day a month where they eat “cheat foods”.  Knowing the very potent chemically-mediated reward system involved with eating foods such as pizza or French fries or ice cream, do you think these are foods that are helpful to eat once a week, or once a month? How much will eating those foods cause you to crave them later, after your “cheat day”? Is it worth it?

From a purely academic perspective, knowing the mechanism also helps explains why metabolically healthy people can lose weight either following a low-fat diet or a low-carb diet, because it is the combination of both carbs and fats that stimulate the reward centers.

Note: a low-carb approach is preferable for people who have have already become insulin resistant or diagnosed with Type 2 Diabetes because they are no longer able to handle more than small amounts of carbohydrate at a time without it significantly impacting their blood sugar (and insulin) levels.

So, knowing that eating carbs and fat together result in a huge release of dopamine and light up the reward-centers of our brain, how should we choose foods differently?

This is where I can help.

Do you have questions about how I can help you eat healthier and reduce food cravings? Would you like information about having me design a Meal Plan for you to help you reach your health and nutrition goals?

Please send me a note using the “Contact Me” tab above and I will reply as shortly.

To our good health,

Joy

References

  1. Di Feliceantonio et al., 2018, Supra-Additive Effects of Combining
    Fat and Carbohydrate on Food Reward, Cell Metabolism 28, 1–12
  2. Carrel, G., L. Egli, C. Tran, P. Schneiter, V. Giusti, D. D’Alessio, and L. Tappy. “Contributions of Fat and Protein to the Incretin Effect of a Mixed Meal.” American Journal of Clinical Nutrition 94, no. 4 (2011):997–1003.
  3. Gross, Lee S., Li Li, Earl S. Ford, and Simin Liu. “Increased Consumption of Refined Carbohydrates and the Epidemic of Type 2 Diabetes in the United States: An Ecologic Assessment.” The American Journal of Clinical Nutrition 79, no. 5 (2004): 774–779.
  4. O’Dea, K., Nestel, P.J., and Antonoff, L. “Physical Factors Influencing Postprandial Glucose and Insulin Responses to Starch” 33, no. 4 (April 1, 1980): 760–65. https://doi.org/10.1093/ajcn/33.4.760.

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Author:

Joy Y Kiddie MSc., RD - I'm a Registered Dietitian in private practice in British Columbia, Canada that provides services in-person in my Coquitlam office, as well as by Distance Consultation (using Skype / telephone).