We know that high-energy food (rich in refined sugars and fats) is addictive and can lead to an eating addiction and obesity. Addiction is a very severe disorder with chronic and relapsing components. People who suffer from addiction show compulsivity, persistence to seek the reward (food), and high motivation to overconsume in some cases.
To study eating addiction, we have developed a mouse model that shows persistence to eat, high motivation for palatable food and resistance to punishment in obtaining the food. We have tested these three characteristics in several genetically identical animals and selected two extreme groups: Mice that are vulnerable to eating addiction and mice that are resilient to it.
Mice have more than 25,000 genes in their genome, and they can be turned on or turned off (‘expressed’ or ‘not expressed’) depending on certain needs or circumstances.
We are now investigating the activation status of a certain type of genes, the ones encoding the so-called microRNAs that are very important as they are involved in regulating the function of other genes. An alteration in the status of one of these genes can have numerous downstream consequences.
In particular, our studies highlighted several microRNA genes that are involved in multiple brain functions, like synaptic plasticity (variation in the strength of nerve signaling) or neuronal development. Now we will test these alterations in patients to try to find convergent abnormalities.
All this work is being done at the Department of Genetics, Microbiology & Statistics (Universitat de Barcelona) and at the Neuropharmacology lab at the Universitat Pompeu Fabra, both based in Catalonia.
Co-authored by Bru Cormand, Judit Cabana, Noelia Fernàndez
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Food is addictive. It has been an addiction that has kept mankind alive for thousands of years. Today, hunger is no longer a problem in the developed world; it is quite the opposite. According to the World Health Organization, worldwide obesity has nearly tripled since 1975. Obesity has reached epidemic proportions globally, with at least 2.8 million people dying each year as a result of being overweight or obese.
In order to maximize the nutritional value, humans are hard-wired to prefer foods that have either a high sugar or fat content. The amount of energy obtained from food is measured in kilocalories (kcal) per gram. Fats have the most energy (9 kcal) and carbohydrates (sugars and starches) have the same amount of energy as proteins (4 kcal). However, these nutrients differ in how quickly they supply energy. Sugars and starches have the advantage of being converted into energy faster than fats and protein. Protein is preferentially used for building and repairing different tissues, not as an energy source.
Once a beneficial adaptation of preferring fast digesting or the most energy-rich nutrients, has now become a risk factor for both physical and also mental health (1), making it an inevitable research focus.
In a recent study at the Yale University School of Medicine (2) it was determined that people not only favour fatty or sugary foods, but place the highest value on those that combine both. Participants (tasked to make monetary bids on different food items) were ready to pay the most for cookies, chocolate, cake and other treats that had both high sugar and also fat content. Equally familiar, liked and caloric fatty (e.g., cheese, salami) or sugary foods (e.g., lollipops) were assigned lower values.
Based on surges of activity, brain scans revealed that foods high in both fat and sugar were more rewarding than foods rich in only one category of nutrient.
Unexpectedly, it was also observed that participants were very accurate at estimating the energy density (kcal) of fatty foods, but poor at estimating the energy density of sugar-containing foods.
Once rare, but nowadays common and abundant treats high in both fat and sugar are most rewarding and therefore can very likely contribute to overeating. In addition, it has turned out to be difficult for people to assess the amount of calories in foods with a high sugar content. These findings taken together can help to understand and also hopefully find new treatment options for people struggling with obesity.
- Hoare E et al (2015) Systematic review of mental health and well-being outcomes following community-based obesity prevention interventions among adolescents. BMJ Open 2015;5:e006586. doi:10.1136/bmjopen-2014-006586
- DiFeliceantonio et al (2018) Supra-additive effects of combining fat and carbohydrate on food reward. Cell Metabolism 28, 1–12. doi:10.1016/j.cmet.2018.05.018
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