Both weekend binges and chronic overconsumption of energy-rich food may lead to similar detrimental effects on gut microbiota, according to researchers from the University of New South Wales in Australia.


The study, which was led by Professor Margaret Morris and the findings of which have been published in Molecular Nutrition and Food Research, used rats to examine the effects of overconsumption during weekend periods on host metabolic parameters and gut microbiota. The researchers compared the abundance of gut bacteria in rats given continuous access to either a healthy diet (termed ‘chow diet’) or an unhealthy diet (termed ‘cafeteria diet’), with an additional group cycled between these diets – healthy for four days and energy-rich foods for three days – over 16 weeks. The standard chow diet provided 12% energy as fat, 20% protein and 65% carbohydrate, whereas the cafeteria diet consisted of the standard chow diet mixed with energy-rich food (such as lard and condensed milk). Several metabolic markers were also measured: body weight, fat mass, blood glucose, insulin and leptin. “This study is the first to compare how continuous or intermittent exposure to an unhealthy diet can impact the composition of the gut microbiota,” said Professor Morris.


The results indicate that intermittent exposure to an energy-rich diet three days a week is sufficient to alter host metabolic parameters and significantly shift gut microbiota towards the profile seen in obese rats consuming the diet continuously. Indeed, the researchers found the microbiota of cycled rats was almost indistinguishable from rats fed a constant unhealthy diet, with both groups’ microbiota significantly different from that of the rats fed a healthy diet. Therefore, both intermittent and continuous exposure to energy-rich food affects gut bacteria in the same way. Ruminococcaceae and Lachnospiraceae taxa were highly responsive to the unhealthy diet and, according to Professor Morris, “would be considered promising targets to treat metabolic disorders such as obesity.”


Disrupted gut microbiota composition is a key feature in the development of obesity and in this study it was correlated with different metabolic parameters. At 16 weeks, rats on the cycled diet were 18% heavier than those on the healthy diet, while leptin and insulin levels in cycled rats stood between those of the rats on healthy or unhealthy diets.


Exposure to energy-rich food not only affected the abundance of microbial species, but also led to changes in microbial metabolic pathways. Any exposure to this kind of food affected microbial fatty acid and flavonoid metabolism pathways. The depletion of the flavonoid pathway is noteworthy, as it not only assists with weight loss, but also exerts neuro-protective functions within the brain.

In conclusion, this study highlights that an intermittent energy-rich diet is likely to be just as bad for gut bacteria as a continuous unhealthy diet. Three days per week is sufficient to extensively shift gut microbiota towards a profile linked to obesity. These results cannot be extended to humans yet, thus clinical trials to study the impact of intermittent dieting on human gut microbiota are needed.



Kaakoush NO, Martire SI, Raipuria M, et al. Alternating or continuous exposure to cafeteria diet leads to similar shifts in gut microbiota compared to chow diet. Mol Nutr Food Res. 2016; doi: 10.1002/mnfr.201500815.