Short term solution, long term problem: Study examines the effects of high-fat diets

26 Jan 2023 --- When following a high-fat diet for a short time period, the brain of rats adapts to react to the type of food that is ingested and balances the calorie intake by reducing the amount of food consumed, according to a US-based rodent model study published in The Journal of Physiology. However, it might increase food intake in the long run as a reaction in the brain could induce an insatiable appetite. 

“Calorie intake seems to be regulated in the short-term by astrocytes. We found that a brief exposure – three to five days – of a high-fat or calorie diet has the greatest effect on astrocytes, triggering the normal signaling pathway to control the stomach. Over time, astrocytes seem to desensitize to high-fat food,” says Dr. Kirsteen Browning, professor of neural and behavioral science at the Penn State College of Medicine, Pennsylvania, US.

The researchers further detail that calorie intake seems to be regulated short-term in the astrocytes – brain cells shaped like stars that regulate various functions in the brain – which controls the signaling pathway between the brain and the gut.

However, the study argues that by continuously eating a diet high in fat or calories, the signaling path gets disturbed.

When foods high in fats or calories are ingested, the astrocytes initially react and trigger the release of gliotransmitters.They continue to stress the importance of understanding the role of the brain in food regulation, as overeating can lead to weight gain and obesity.

Obesity is a global health concern. In England, 63% of adults are considered overweight – half of which are obese – and one-third of children leaving primary school are overweight or obese.

Short vs. long-term
When foods high in calories and fats are ingested, the astrocytes initially react, triggering the activation and release of gliotransmitters – chemicals that excite nerve cells, enabling normal signaling pathways to stimulate neurons controlling the stomach.

These signals ensure that the stomach contracts correctly – filling and emptying – when responding to and digesting food. However, the astrocytes are disrupted, and so is the cascade that delays the digestive system.

Therefore, following a high-fat diet for a prolonged time might trigger hyperphagia – feelings of uncontrolled hunger – and result in weight gain from an excessive calorie intake.

“Around 10-14 days of eating a high-fat or calorie diet, astrocytes seem to fail to react, and the brain’s ability to regulate calorie intake seems lost, which disrupts the signaling to the stomach and delays how it empties,” Browning adds.

“We have yet to find out whether the loss of astrocyte activity and the signaling mechanism is the cause of overeating or if it occurs in response to the overeating. We are eager to determine whether it is possible to reactivate the brain’s apparently lost ability to regulate calorie intake. If this is the case, it could lead to interventions to help restore calorie regulation in humans,” she details.

Prior research in weight management
The aim of ketogenic diets – high in fats and protein while low in carbohydrates and no added sugar – is for the body to reach a ketosis state, a process where it does not have enough energy to burn, resulting in fat burn due to increased metabolism. Browning highlights the need to determine if the loss of astrocyte activity and the signaling mechanism is the cause of overeating or if it occurs in response to the overeating.

A previous study into the keto diet showed its benefits for muscle restoration, but in terms of weight loss, there were no results in keeping the weight off in the long run.

Another study demonstrated that high-protein diets and specific antibiotics could prevent weight gain after dieting, as most individuals gain back the weight lost. The findings detail that an increase of Lactobacillus and its metabolites after dieting enhanced intestinal lipid absorption leading to quick fat accumulation. In contrast, high-protein diets inhibit the growth of the bacteria.

According to experts, weight management has seen a transformation during the COVID-19 pandemic from focusing on weight loss to a holistic approach of striving for better mental health alongside healthier eating patterns.

By Beatrice Wihlander

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