Is the Combo of Carbs and Fats Duping Your Brain.. and Diet?

Carbs Fats Combination

Is one of our bigger diet problems when we mix carbs and fats together? Because our brains sure get confused by the situation… Image Courtesy Cell Metabolism[1]

It’s no secret that the best-tasting foods are usually dosed with a higher amount of both fats and carbs. They’re also almost universally processed foods, with this combination rarely occurring in nature. Sure, many claim to love a grilled chicken salad from time to time, but if calories and macros didn’t matter, would you still have that salad instead of a slice of cake, potato chips, or even an entire batch of warm chocolate chip cookies?

According to a new research, the answer is no!

A recent study shows that the combination of a high fat and high carbohydrate diet can directly lead to overeating, by desensitizing our body’s ability to properly evaluate the nutrient density of food.[1]

And even crazier – the researchers showed that we are terrible at estimating energy from carbohydrates!

Sure, we know eating a surplus of carbs and fats together will lead to weight gain. And we know that protein is where the changes are in body composition itself.[2-4]

But now we have some direction as to why so many people are way better off with either low-carb or low-fat diets… and why things can get out of control when they allow for both.

Is Your Brain Programmed to “Count Macros”?

Junk Food

As we have “known” for a while, a combination of high fats and high carbs in a diet could be detrimental.

In a sense, it is. A recent study suggests that people are more easily able to estimate the energy density of fat or carbohydrate foods over foods with both fat AND carbohydrates. This effect is associated with the functional connectivity between the brain’s visual (fusiform gyrus) and valuation (ventromedial prefrontal cortex) areas. The study shows that foods that are high in fat and carbohydrates are, calorie for calorie, valued more than foods containing only fat or carbohydrates![1]

Why? Apparently, this effect results in recruitment of a person’s central reward circuits. Essentially, we associate foods with higher carbs and fats in combination with one another to be more rewarding. Further, our body learns that fat is a more caloric dense option, and therefore may be preferred in times of energy depletion (note, for example, that hungry wild animals on a hunt fight for the fatty tissue first).

Consider the Average “Cheat Meal” – Carbs and Fats Combined!

This seems to make sense with the eye test. Clearly, our brain fires pleasure signals when we see a “cheat meal”, knowing how good it will taste. More often than not, that cheat meal will have a combination of carbs and fats in conjunction with one another. Some of the most glorified “pleasure” foods are usually a high combination of fats and carbs:

Cheat Meal

Consider the effects of cheat meals, if used too often and in a non-strategic manner.

  • Burger and Fries – high fat beef and cheese, with potatoes fried in oil.
  • Pizza – Bread with fatty meats and cheese.
  • Pasta – Cream, oil, cheese, etc…
  • Cookies – sugar, butter, oil, etc…
  • Potato Chips – Potatoes, oil, and salt!
  • Chocolate – Sugar and fat!

You get the point. Sure, you can make healthier versions, but your average restaurant isn’t going to measure the oil or butter they use on a food scale, and even worse, those restaurants and processed food manufacturers use seed oils that are high in inflammatory omega-6 fatty acids. Even if you count calories and macros, you generally have to assume your macros will crushed if eating out and enjoying any of the above stuff.

Protein can’t be ignored…

On top of that, the above foods are often low protein but usually not zero protein, which may keep your body asking for more and more as it tries to “leverage protein”, a nutrient it really does need![8]

How Did This Get Measured?

In this study, participants were given five Euros and told they could bid on food items. They were only bidding against a computer, with random bid amounts. The study gets interesting here, as the data shows that participants were given three distinct options:

Carbs Fats Valuation

An overwhelming amount of particpants opted to have a food that was high in both fat and carbs, rather than food that was in only one of those macros.[1]

  1. a food primarily consisting of carbohydrates (i.e., crackers);
  2. a food primarily consisting of fat (i.e., cheese); and
  3. a food consisting of both carbohydrates and fats (i.e., sandwich cookie, candy, etc…)

All of the foods were similar in caloric density. Brain activity was measured throughout the testing.[1]

Across the board, participants’ “reward circuits” were more active when bidding on the fat and carbohydrate combined food item. One possibility is that the “postingestive signal” (which conveys information about the nutritive value of fat) is successfully integrated with visual information about foods to determine caloric value, whereas the value of carbohydrates may stem from factors such as flavor or the food’s visual presentation.[1]

The evolutionary perspective provides the most insight

The best explanation for the study’s results are actually one that weren’t even proposed by the researchers. Looking at it from an evolutionary lens, the brain should highly value when carbs and fats can be seen together. Because this is a rare moment that allows for fat storage, which was historically an extremely protective survival mechanism.

When are carbs and fats naturally found together?

Consider the two times when carbs and fats are found together:

  1. Breastmilk

    Built for the most important “bulking season” of our lives, breastmilk is actually pretty low in protein – around 6% – but plenty high in carbs and fats! This is because newborn humans need to pack on as much weight as possible after birth, even if it’s in the form of added bodyfat!

  2. During the autumn harvest

    Autumn is a time when animals fatten up and fruits and nuts harvest. Carbs and fats together. It’s also the time when animals must prepare for hibernation and the cold winter.

    Meanwhile, consider the mighty acorn. A favorite “bulking tool” of squirrels, deer, and several other animals, these nuts have “obesogenic” macronutrient ratios high in fats, carbs, but relatively low in protein. Very few natural foods have these types of macros!

    It’s no surprise that our evolutionary “bulking seasons” also correlate with the only times when carbs and fats appear in unison. But it’s never year round!

Pioneered by Cian Foley, who urges dieters to avoid “autumnal eating” (or “eating for the winter”),[9] the above scenarios show the best reasoning for our brains to “freak out” when confronted with carbs and fats together – it’s a signal that winter is coming, and we better put our fat on now.

Of course, we no longer have evolutionary pressures – but our lizard brains don’t know that. They simply know to pack on the pounds to get ready for the harsh winter. Our brains are trying to protect us. But when that winter never comes… thirty years of this later, and you have an overweight population (at best).

Researcher Theory: Are Artificial Sweeteners Ruining Our Brain’s Ability To Value Carbohydrate Calories?

Artificial Sweeteners

Artificial sweeteners are nice to avoid excess calories but be warned it may be tricking your brain!

Another (unlikely) possibility proposed by the researchers is that recent increases in artificial sweeteners in modern diets can degrade how our brain associates differences between carbohydrate-containing foods and its actual energy density. Essentially, this creates an impaired ability to estimate calories correctly.[1]

This makes a bit of sense, but doesn’t account for issues that occur such as when animals become obese from eating human trash (our junk food) or the evolutionary angle listed above. I am extremely confident that this reward circuit experiment would still work on someone who’s never been exposed to artificial sweeteners – there’s just something to foods with both fats and carbs:

Why does the brain view fats and carbs differently, from an energy point of view?

This data suggests that the association between food as a reward and food as an energy dense option will differ for fat and carbohydrate (Figure 2). For fatty foods, our willingness to pay is tightly coupled to energy density and self-reported “food liking”. Although both food liking and energy density are associated with willingness to pay, mediation analyses indicate that these factors contribute independently to reward value.[1]

Carbs Fats Figure 2

Figure 2[1]

In contrast to fats, for carbohydrate-containing foods, our willingness to pay is positively related to self-reported food liking, but not necessarily energy density. Although individuals are very accurate at estimating the energy density of fatty foods, they are poor at estimating the energy density of carbohydrate-containing foods.

This may indeed stem from our abuse of sugar and other sweeteners. We are essentially tricking our body about the energy density of food we eat, and now we’re clueless when it comes to the true value of our carbs! An argument to explain this is that throughout the course of evolution, we’ve had high amounts of carbohydrates less readily-available than fats and proteins, and aren’t adapted to having year-round carbohydrate availability (and certainly not year-round carb+fat availability, traditionally only found in autumn and breastfeeding).

How does this make us fat?

Outside of inducing overeating from a caloric perspective, there’s something else to consider: the fact that the fat eaten with carbs will be stored as fat! Reason being, when you ingest carbohydrates (and/or spike your insulin), you stop oxidizing fat![10,11] The carbohydrates get “oxidative priority” and beta-oxidation of fat halts to a standstill until the glucose is taken care of and insulin levels fall.

For some, this almost never happens anymore, with round the clock eating. Which slowly turns into lifelong weight gain for those who cannot stop eating these combinations.

Most low-carb dieters don’t fully understand this point either – it takes a ton of carbohydrates on their own to induce fat storage (like 500g worth!).[12] The carbs aren’t what get stored as fat – it’s the fats eaten alongside them that do! This is why low-fat diets generally work (although they are often more difficult and lead to less desirable metabolic and lipid profile changes for most individuals).

Long story short – eat carbs and fats together, your body has to burn the carbs, and it has to store the fats while it deals with the carbohydrate burden. Keep them separate or deal with the fact that fat loss won’t be happening for a while!

What does this all mean?

This study produced two findings that are relevant to help understand why we make certain food choices:

  1. Fats and carbs are more mentally “rewarding”

    First, this is the first demonstration that foods containing both fat and carbohydrate are more rewarding, calorie for calorie, than those containing only fat or only carbohydrate. The study also proves this via brain monitoring. It proved that people will have a more “reward” like effect when given food options consisting of carbs and fats, rather than one or the other.[1]

  2. It’s easier to estimate energy density of fatty-only foods

    Second, this study revealed that individuals are better able to estimate the energy density of fat foods, compared with carbohydrate foods, and fat combined with carbohydrate foods.[1]

Brain Monitoring Carbs Fats

Brain monitoring during this study proved that “rewards circuits” were firing across the brain in response to fat and carb foods, more so than fat foods or carb foods alone.

Both findings support and extend work from animal models indicating that these two energy sources (carbs and fats) have distinct pathways for conveying nutritive value to our central nervous system. This helps to guide our food choice and proves the need to further study how we make certain macronutrient decisions.[1]

Studies in mice show that dopamine release as result of food, will differ depending on how that food is used as an energy source.[5-7] This suggests that our gut to brain pathways that drive fat and carbohydrate reward, may differ. The data from this study seems to support this proposal.[1]

The Protein Question

Your next question may be “where does protein fit into this?” My take? It’s most important, and binges will occur most when a food (such as ice cream) has some protein, teasing the body. This is due to protein leverage, as discussed above.[8]

So regardless of how our brains “value” our proteins, when formulating a diet, it’s the one thing that should always be set to at least a minimum, and preferably within a reasonable window above that minimum.

Low-Fat or Low-Carb for fat loss: Choose the one that works best for you!

After protein comes the carbs and fats game – and if we’ve learned anything here, it’s that choosing either low-carb or low-fat are critically important, especially if not weighing food and counting calories like a hawk.

When many dieters allowed to have both “normal fats” and “normal carbs”, things can spiral out of control quickly. See the hyperphasia section above. For many of us, we may be better if that addictive bag of chips with fats and carbs is completely off limits.

Point being, if you still want a “balanced diet”, then you need to track macros, because the research now shows that you’re probably not as good at estimating a food’s energy value as you would think!

Takeaway – High Carbs and High Fat Together Will Likely Lead to Overeating.

We may have messed with our brain’s ability to properly evaluate macronutrients, but chances are, our bodies never evolved to deal with too many high-fat and high-carb foods in the first place! They’re for a special occasion — bulking season before winter!

If you track calories and macros, then this shouldn’t be an issue, but most don’t do that over the long haul. It’s interesting to see that our body has a unique natural means of evaluating the nutritional value of food and can influence our food decisions via this mechanism. It’s even more interesting to see how badly we can fail at it with some “unnatural” foods – especially when there’s year-round exposure!

By combining the two food options, we may be doing more harm than we realize to our bodies – and it starts with a confused brain. The study indicates that combining fat and sugar will increase the reward value of foods, regardless of its caloric value, preference, and portion size. Essentially, the combination of both food types disrupts the ability to accurately estimate the energy density of fatty foods. By implication, a greater reward signal is generated by foods high in both fat and carbohydrates. We know the dopamine release from eating “junky” foods leads us to want more… and this hasn’t even touched on the leptin/grehlin cycles either!

This may be one theory that explains how processed foods high in fat and carbohydrates leads to overeating. Your thoughts in the comments. Do you avoid foods combined with high fats and high carbs? Is it one or the other, or can you maintain a balanced diet without living on MyFitnessPal to count macros?


  1. DiFeliceantonio, Alexandra G., Coppin, Géraldine., Rigoux, Lionel., Thanarajah, Sharmili Edwin., Dagher, Alain., Tittgemeyer, Marc., Small, Dana M., Supra-Additive Effects of Combining Fat and Carbohydrate on Food Reward.
  2. Parker, B. et al; “Effect Of A High-Protein, High-Monounsaturated Fat Weight Loss Diet On Glycemic Control And Lipid Levels In Type 2 Diabetes”; Diabetes Care; 25.3 (2002): 425-430;
  3. Evans, Ellen M, et al; “Effects of Protein Intake and Gender on Body Composition Changes: A Randomized Clinical Weight Loss Trial”; Nutrition & Metabolism 9 (2012): 55;
  4. Leidy, H. J. et al; “The Role Of Protein In Weight Loss And Maintenance”. American Journal of Clinical Nutrition 101.6 (2015): 1320S-1329S;
  5. Tellez, L.A., Han, W., Zhang, X., Ferreira, T.L., Perez, I.O., Shammah-Lagnado, S.J., van den Pol, A.N., and de Araujo, I.E. (2016). Separate circuitries encode the hedonic and nutritional values of sugar. Nat. Neurosci. 19, 465–470;
  6. Tellez, L.A., Medina, S., Han, W., Ferreira, J.G., Licona-Limon, P., Ren, X., Lam, T.T., Schwartz, G.J., and de Araujo, I.E. (2013b). A gut lipid messenger links excess dietary fat to dopamine deficiency. Science 341, 800–802;
  7. Tellez, L.A., Ren, X., Han, W., Medina, S., Ferreira, J.G., Yeckel, C.W., and de Araujo, I.E. (2013c). Glucose utilization rates regulate intake levels of artificial sweeteners. J. Physiol. 591, 5727–5744.
  8. Simpson S, Raubenheimer,D; “Obesity: the protein leverage hypothesis”; Obes Reviews; 6(2):133-42; May 2005;
  9. Foley, Cian; “Don’t Eat For Winter”;
  10. Sidossis, L, et al; “Glucose and insulin-induced inhibition of fatty acid oxidation: the glucose-fatty acid cycle reversed”; American Journal of Physiology; 270(4 Pt 1):E733-8; April 1996;
  11. Bonadonna, R; “Dose-dependent effect of insulin on plasma free fatty acid turnover and oxidation in humans”; The American Journal of Physiology; 259(5 Pt 1):E736-50; November 1990;
  12. Acheson, K J, et al; “Glycogen storage capacity and de novo lipogenesis during massive carbohydrate overfeeding in man”; The American Journal of Clinical Nutrition; Volume 48, Issue 2; August 1988; Pages 240–247;
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