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Mind over Macronutrients: How Cutting Fats vs. Carbs Affects the Brain

Weight loss is a journey that many embark on, with a plethora of diet options promising results. While the most debated diet dilemma is whether to cut carbs or fats, a recent study dives deeper into understanding the underlying neurological implications of such decisions.

The Science Behind Eating Habits

Dopamine, a neurotransmitter pivotal to our eating habits and weight regulation, plays an intriguing role in our food choices. Often misconstrued merely as a pleasure inducer, dopamine is steered by subconscious cues that determine food's reward value, governing behaviors such as motivation and compulsion. Intriguingly, people with obesity tend to have lower dopamine production, and the neurotransmitter levels might correlate with body fat. Hence, dopamine doesn't just control our joy of savoring food; it potentially influences our cravings and dietary preferences.

A Deep Dive into Dietary Choices

A comprehensive study conducted at the Metabolic Research Unit at the NIH Clinical Center sought to understand the brain's reaction when given a reduced-fat versus a reduced-carbohydrate diet. This study observed 17 adults with obesity over two distinct 14-day sessions.

The Protocol:

Standard Diet Phase: The participants began with 5 days of a standard diet - 50% carbohydrates, 35% fat, and 15% protein.

  1. Dietary Restriction Phase: Following the initial phase, participants were subjected to either the reduced-fat or reduced-carbohydrate diet for six days.

  2. Free-choice Phase: The last three days saw participants having the freedom to select foods from a vending machine.

  3. Repeat with Alterations: After a 2-4 week hiatus, the same participants were subjected to the opposite diet of what they began with.

Findings: The Brain on Diet

Utilizing advanced imaging techniques, the study discovered:

  • Neurological Response: Only the reduced-fat diet led to decreased activity in the brain's reward regions, specifically the striatum, when participants viewed food images.

  • Dopamine Dynamics: An interesting finding was the reduced D2 dopamine receptor binding potential following the reduced-fat diet. This indicates that the reduced-fat diet might increase the brain's dopamine activity, explaining the decreased neural response to food cues.

  • Food Choices Post Diet: Only after the reduced-fat diet period were participants more inclined towards foods high in both, carbohydrates and fat. Moreover, there was an increased consumption of sugar-sweetened beverages after the reduced-fat diet.

Implications and Theories

While both reduced-fat and reduced-carbohydrate diets influence metabolic and hormonal responses, the reduced-fat diet had a more pronounced negative effect on brain reward pathways. Some theories suggest that the reduced-fat diet might boost tonic dopamine, skewing the balance between different dopamine responses and enhancing the longing for rewarding foods. Other potential mechanisms proposed include the increased production of oleoylethanolamide from dietary fats and the decline in post-meal plasma triglycerides.

In contrast, the reduced-carbohydrate diet didn't substantially affect brain dopamine.

In Conclusion

Our understanding of diets goes beyond shedding pounds; it's an intricate web of physiological and neurological pathways. While it would be exciting to see future studies with larger numbers of people, as well as to include non-obese participants, this interesting study emphasizes already that when considering brain reward responses, all calories aren't created equal.

Macronutrient composition significantly influences our brain's reaction and our subsequent dietary choices. As dietary debates continue, it's clear that our brain plays a pivotal role in our food choices and potential weight-loss success!


Darcey, V. L., Guo, J., Courville, A. B., Gallagher, I., Avery, J. A., Simmons, W. K., Ingeholm, J. E., Herscovitch, P., Martin, A., & Hall, K. D. (2023). Dietary fat restriction affects brain reward regions in a randomized crossover trial. JCI Insight, 10(1172), e169759


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