Scientists have found that extra nitrogen from a high carbohydrate, low protein diet can allow bacteria to grow in a way that compliments an animal's gut.
Kemal Atlay

25 Nov 2016 - 4:06 PM  UPDATED 25 Nov 2016 - 4:06 PM

A high carbohydrate and low protein diet, where the amount of nitrogen consumed is restricted, is the most beneficial for our gut health, according to a new study.

While numerous en vogue diets, like paleo and ‘I Quit Sugar’ have advised us to avoid the delicious starchy carbohydrates of bagels and pasta and live a fulfilling life eating lean proteins, it appears that cutting carbs might not be the answer to healthy eating.

Researchers from the University of Sydney’s Charles Perkins Centre studied the relationship between different diet strategies and gut health and found that nitrogen from protein plays a crucial role in regulating gut bacteria. The study was published in Cell Metabolism.

Although nitrogen is one of the essential building blocks of cells and tissues in the body, it can also act as a ‘fertiliser’ that promotes uncontrolled growth of bacteria in the gut, known as microbiota or 'the microbiome'.

“What we have found is a unifying mechanism for how diet drives a good and a bad microbiome,” lead author Associate Professor Andrew Holmes tells SBS Science.

“What we have seen is that basically when you eat too much, in particular when you eat too much of protein, what happens is that you encourage ‘weeds’.”

The findings are from an extensive long-term study where 25 different diets with varying ratios of cabohydrates, fat and protein were tested on 858 mice. The outcome revealed that a high carbohydrate and low protein diet promoted a healthy relationship between the bacteria in the gut and the host animal.

It was previously reported in this same experiment that the high carbohydrate, low protein diet promoted the production of the 'fountain of youth' hormone called FGF21.

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“If you’ve got a lot of protein in your diet, then that translates to a lot of nitrogen and amino acids ending up in your gut and that means that the bacteria are being fertilised,” Holmes says.

Vice-versa, a high protein and low carbohydrate diet meant that the extra nitrogen allowed the bacteria to grow in a way that negated the need to cooperate with the animal’s intestine and body for nutrition.

Holmes explains that with a high carbohydrate and low protein diet, the scales are tipped further towards beneficial relationship between our microbiota and our body when there are more complex carbohydrates that have a high fibre content and are harder to break down.

This is important because gut health can greatly affect other body systems and has the potential to improve metabolic health and, as a result, promote healthy ageing and longevity.

For example, uncontrolled gut bacteria growth can cause our immune system to work harder to maintain gut health, which can result in a state of chronic inflammation - this has been linked to health issues associated with obesity.

“It’s a really robust story that a low protein, high carbohydrate [diet] shifts every part of the animal system, so what our cells and tissues are doing, what our microbes are doing – [they] all operate together in ways that are consistent with improved longevity and metabolic health,” says Holmes.

He also explains that a paleo diet, or “lifestyle”, that manages to preserve this high carbohydrate, low protein balance by reducing intake of processed food, as opposed to cutting out whole food groups like dairy to shift the equation to more protein means it can still be beneficial to gut health. 

Dr Duane Mellor, a nutrition expert from the University of Canberra, says the findings are exciting but cautioned against misinterpreting the implications for human health.

“It’s an interesting paper, I think we have to bear in mind that it’s a mouse study and the limits of sort of using mouse diet patterns compared to human diet patterns because our natural diets are very different,” he tell SBS Science.

He also echoes Holmes’ concerns about how we view the paleo diet but says those who strictly adhere to consuming more animal meat and protein have misinterpreted it.

“I think it’s possibly interpretation of some of these diets where they’re cutting out whole food groups, so they might not be getting the fibre intake, they make be limiting things like legumes… so it’s not really the hunter-gatherer style of eating,” he says.

“I think the problem is not the concept of wanting to eat healthy and eating less refined food… it’s when it started becoming restricted on legumes and possibly dairy, that’s when it becomes a little bit more challenging and not entirely necessary.”

Holmes explains that the next step in the research will be to explore what happens to our gut bacteria when you manipulate the complexity of carbohydrates consumed, but says the overall message is simple.

“Keep your protein as close to your daily requirements and no more than you need, and keep your carbohydrate profiles complex rather than simple,” he says.

While bagels are probably not the best option, given their large amount of sugar, but according to the Charles Perkins Centre, whole-wheat toast is still on the breakfast menu.

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