Obese Men Need Extra Energy to Resist Food Craving

• A study using positronic emission tomography published in the International Journal of Obesity found that obese men need extra energy to resist the desire to eat
• Just presenting men with their favorite foods increased the use of glucose in several areas of the brain, regardless of obesity
• The brains of obese men required more energy to inhibit food cravings than the brains of men who were not obese

We have all experienced situations where we really, really want to eat something we shouldn’t. This experience is probably best known to individuals trying to lose weight by simply eating less. This struggle with the desire to eat might be completely invisible to outside observers. It only happens in our minds. But does that psychological struggle to avoid eating require extra energy? Most importantly, is this energy expenditure greater when the struggle is harder? A group of researchers conducted a study back in 2020 to find out.

 

This struggle with the desire to eat might be completely invisible to outside observers. It only happens in our minds. But does that psychological struggle to avoid eating require extra energy?

 

Hunger, food intake control and obesity

Our body needs food to survive. However, it is also possible to eat more than we need. Our body has a complex neuropsychological mechanism that controls this balance (Atasoy et al., 2012). This mechanism involves a complex interplay of signals from the digestion system, hormones like leptin and ghrelin (Hedrih, 2024b), and processes in the brain, primarily in the hypothalamus. The hypothalamus contains a set of neurons known as hunger neurons (agouti-related peptide neurons) that activate food-seeking and intake behaviors when triggered. On the level of subjective experiences, the described processes produce the sensation of hunger when we need food and satiety when we have eaten enough  (Hedrih, 2024a) (more about neuropsychological mechanisms can be found in CNP’s NP 100 Series Introductory Certificate in Nutritional Psychology). 

However, studies have shown that lack and abundance of required nutrients are not the only things that trigger feelings of hunger and satiety. Hunger can be triggered by stress, the smell or taste of delicious food, our eating habits, and many other factors (Hedrih, 2023; Isherwood et al., 2023; Swami et al., 2022).

 

The lack and abundance of required nutrients are not the only things that trigger feelings of hunger and satiety

 

This food intake regulation mechanism can also become dysregulated, making us believe that we need more food when we actually do not. When this happens, we will tend to start overeating and, in time, become overweight or obese (Ikemoto et al., 1996; Pujol et al., 2021).

 

This food intake regulation mechanism can also become dysregulated, making us believe that we need more food when we actually do not

 

Food reward system

Because food is crucial for survival, our brains have evolved to treat food as a strong natural reward. Its rewarding characteristics become particularly strong when we have not eaten for some time. Even just showing food to a person who wants to eat, it increases the activity and energy expenditure in the orbitofrontal cortex region of the brain (Wang et al., 2020), a region that plays a key role in regulating our food intake. The hungrier we are, the stronger the increase in metabolism in this part of the brain will be.

 

Even just showing food to a person who wants to eat it increases the activity and energy expenditure in the orbitofrontal cortex region of the brain

 

Studies indicate that obese individuals are more sensitive to hunger than normal-weight individuals. The regions of their brains that process rewards become more active when they see food (Devoto et al., 2018). But does this mean their brains will also be more active when they resist eating the food they like?

 

Obese individuals are more sensitive to hunger than normal-weight individuals

 

The current study

Study author Gene-Jack Wang and his colleagues hypothesized that obese individuals would have decreased activation in the orbitofrontal cortex region of the brain, in the striatum, and the insula when resisting the desire to eat appealing food. They would also have increased activity in the anterior cingulate cortex. They conducted a study to test whether this is really the case (see Figure 1).

 

Figure 1. Hypothesized regions of the brain in obesity

 

The study procedure

The study participants were 16 obese and 11 non-obese men. The authors first asked them to fill out a questionnaire related to their favorite foods and food smells and to rate a list of foods for desirability. Participants also completed an assessment of eating behaviors (the Three Factor Eating Questionnaire).

On three different days, study participants underwent positron emission tomography (PET) scans of their brains using fluorodeoxyglucose as the radiotracer. Fluorodeoxyglucose is similar to glucose but has one atom replaced by the radioactive isotope fluorine-18. This allows researchers to detect fluorodeoxyglucose using the PET scanner and assess the level of metabolic activity in the scanned brain regions – more active regions will use more glucose, hence more fluorodeoxyglucose.

On the first day, the study authors placed cotton swabs impregnated with participants’ favored foods on participants’ tongues 15 minutes before the scan began and throughout the scanning procedure. In this way, participants could taste the food but not eat it. They would also warm participants’ favorite foods and present them one after another to each study participant. At the same time, participants verbally described their favorite foods and how they like to eat them. Participants were hungry during the procedure, having not eaten anything since the previous evening.

On the second day, the study authors applied the same procedure and told participants to inhibit their food desire before the food presentation began. On the third day, participants underwent PET scans without any food presentation (see Figure 2).

 

Figure 2. Study procedure (Wang et al., 2020)

 

Food stimulation increases glucose metabolism in several brain regions

When participants from both groups were presented with food, their glucose metabolism increased in the brain’s inferior and superior frontal gyrus regions, the default mode network, and the cerebellum. Attempting to suppress the desire to eat the food reduced metabolism in the right subgenual anterior cingulate, orbitofrontal areas, bilateral insula, and temporal gyri areas (see Figure 3).

 

Figure 3. Food stimulation increases glucose metabolism in several brain regions

 

The brains of obese men use more energy to inhibit the desire to eat

When study authors instructed participants to inhibit their food desire (on day 2), this led to an increase in metabolism in the pregenual anterior cingulate cortex and caudate areas of the brains of obese men (compared to the same situation without inhibition). In the same condition, non-obese men showed decreased metabolism in these areas. Obese men who reported stronger changes in food desire after attempting to inhibit it showed lower changes in the level of metabolic activity in this brain area compared to the condition with food stimulation but with no inhibition (see Figure 4).

 

Figure 4. Effect of inhibiting food desire in obese men

 

Conclusion

When attempting to inhibit their food desire, obese men showed higher activity in two areas of the brain involved in self-regulation and emotional rewards. This shows that, in obese men, inhibiting food desire is an active process that requires extra energy. 

 

When attempting to inhibit their food desire, obese men showed higher activity in two areas of the brain involved in self-regulation and emotional rewards

 

This likely means that obese individuals need to commit greater psychological effort to achieve the same level of control over eating behaviors compared to nonobese individuals. The difference in the effort required to control food intake is a factor that should be taken into account when planning weight loss programs.

The paper “Inhibition of food craving is a metabolically active process in the brain in obese men” was authored by Gene-Jack Wang, Ehsan Shokri Kojori, Kai Yuan, Corinde E. Wiers, Peter Manza, Christopher T. Wong, Joanna S. Fowler, and Nora D. Volkow.

Important note. In the original paper, figure (3b), which presented the key finding (the increase in metabolic activity in the pregenual anterior cingulate cortex and caudate areas of obese men), shows results that are the opposite of what was described in the text of the paper (i.e., it shows an increase in nonobese participants when inhibiting the desire to eat, and a decrease in the obese group). This text relied on the study authors’ textual interpretation of results and assumed that the designations of the two groups in the figure were inverted. If this was not the case, then this part of the results presented in this text is incorrect.

 

References

 

Atasoy, D., Betley, J. N., Su, H. H., & Sternson, S. M. (2012). Deconstruction of a neural circuit for hunger. Nature, 488(7410), 172–177. https://doi.org/10.1038/nature11270 

Devoto, F., Zapparoli, L., Bonandrini, R., Berlingeri, M., Ferrulli, A., Luzi, L., Banfi, G., & Paulesu, E. (2018). Hungry brains: A meta-analytical review of brain activation imaging studies on food perception and appetite in obese individuals. Neuroscience & Biobehavioral Reviews, 94, 271–285. https://doi.org/10.1016/j.neubiorev.2018.07.017

Hedrih, V. (2024a, March 4). Researchers Identify Neural Pathways Transmitting Anti-Inflammatory Effects of Hunger. Nutritional Psychology. https://www.nutritional-psychology.org/researchers-identify-neural-pathways-transmitting-anti-inflammatory-effects-of-hunger/ 

Hedrih, V. (2024b, May 20). Do Gut Microbiota Play an Important Role in Regulating Food Intake and Satiety? Nutritional Psychology. https://www.nutritional-psychology.org/do-gut-microbiota-play-an-important-role-in-regulating-food-intake-and-satiety/ 

Hedrih, V. (2023). Are Hunger Cues Learned in Childhood? CNP Articles. https://www.nutritional-psychology.org/are-hunger-cues-learned-in-childhood/ 

Ikemoto, S., Takahashi, M., Tsunoda, N., Maruyama, K., Itakura, H., & Ezaki, O. (1996). High-fat diet-induced hyperglycemia and obesity in mice: Differential effects of dietary oils. Metabolism, 45(12), 1539–1546. https://doi.org/10.1016/S0026-0495(96)90185-7 

Isherwood, C. M., van der Veen, D. R., Hassanin, H., Skene, D. J., & Johnston, J. D. (2023). Human glucose rhythms and subjective hunger anticipate meal timing. Current Biology, 33(7), 1321-1326.e3. https://doi.org/10.1016/j.cub.2023.02.005 

Pujol, J., Blanco-Hinojo, L., Martínez-Vilavella, G., Deus, J., Pérez-Sola, V., & Sunyer, J. (2021). Dysfunctional Brain Reward System in Child Obesity. Cerebral Cortex, 31, 4376–4385. https://doi.org/10.1093/cercor/bhab092 

Swami, V., Hochstöger, S., Kargl, E., & Stieger, S. (2022). Hangry in the field: An experience sampling study on the impact of hunger on anger, irritability, and affect. PLOS ONE, 17(7), e0269629. https://doi.org/10.1371/JOURNAL.PONE.0269629 

Wang, G.-J., Shokri Kojori, E., Yuan, K., Wiers, C. E., Manza, P., Wong, C. T., Fowler, J. S., & Volkow, N. D. (2020). Inhibition of food craving is a metabolically active process in the brain in obese men. International Journal of Obesity, 44(3), 590–600. https://doi.org/10.1038/s41366-019-0484-z