• The main source of fats consumed in the high-fat diet was soybean oil: a good source of healthy fats. (EyeEm/Getty Images)
A low-carb, high-fat diet may be great to help you lose weight. But, according to a new international study, this diet could damage your good gut bacteria and may cause inflammation throughout your body in the long term.
By
Yasmin Noone

21 Feb 2019 - 11:29 AM  UPDATED 21 Feb 2019 - 11:37 AM

Going on a high fat diet to lose weight may help you successfully shed the kilos but according to a new international study on Chinese adults, it could wreak havoc on your gut and trigger inflammation throughout your body in the long term.

The world-first study, published online in the journal Gut this week, shows that exchanging a low-fat, high-carb diet for one that’s high in fats and low in carbohydrates may cause unfavourable changes in the gut bacteria and inflammatory triggers.

“Compared with a lower-fat diet, long-term consumption of a higher-fat diet appears to be undesirable owing to changes in gut microbiota, faecal metabolomic profiles and pro-inflammatory factors for healthy young adults…” the study reads.

The main sources of carbs in the diet were white rice and bread, while the main fat consumed was soybean oil: a good source of healthy fats, like omega-3 fatty acids and polyunsaturated fats. 

These negative health effects were observed at the end of the six-month study, even though the high-fat, low-carb eating plan proved to be successful for weight loss. The main sources of carbs in the diet were white rice and bread, while the main fat consumed was soybean oil: a good source of healthy fats, like omega-3 fatty acids and polyunsaturated fats. 

“It should be noted that the intake of polyunsaturated fatty acids was relatively high in the higher-fat diet group (24 per cent of total energy) owing to exclusive use of soybean oil, which is rich in n-6 polyunsaturated fatty acids,” the paper reads. “A higher intake of n-6 polyunsaturated fatty acids has been reported to have pro-inflammatory effects.”

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The paper’s authors – Chinese, Australia, USA and New Zealand researchers – highlight that the low-fat, high-carb diet was popular in China 30 years ago when obesity was rare.

They say this is in stark contrast to the current obesity situation today, with a high-fat, low-carb diet now being more common. According to the Global Burden of Disease report, China had the highest numbers of obese children in the world with 15.3 million in 2015. The nation also has the world’s second largest population of obese adults – 57.3 million.

“[In China], the nutritional transition from the traditional low-fat, high-carbohydrate diet to a diet relatively higher in fat and lower in carbohydrate has been associated with a dramatic increase in the risk of obesity, type 2 diabetes and cardiovascular diseases in the past 30 years,” the authors say.

The authors add that these results illustrate the need for people of all countries to curb dietary fat intake, especially in developed countries like Australia, where fat intake is already high.

The results showed that after six months, participants in all three groups lost weight. People following the low-fat diet dropped the most kilos.

How the results unfolded

The study was conducted on 217 healthy, young Chinese adults. The researchers split the participants into three dietary groups and got them to follow a designated diet for six months.

The three diets were low fat (20 per cent of energy intake); moderate fat (30 per cent of energy intake); and high fat (40 per cent of energy intake). Fibre and protein content stayed consistent.

The diet’s impact on gut bacteria and inflammatory triggers was assessed in blood and faecal samples taken at the start and end of the six months.

The results showed that after six months, participants in all three groups lost weight. People following the low-fat diet dropped the most kilos.

However, the numbers of these beneficial bacteria fell in the high fat diet group, while numbers of ‘unhelpful’ bacteria that have been found in the guts of people with type 2 diabetes increased.

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The higher fat diet was associated with significant and potentially detrimental changes in long chain fatty acid metabolism, resulting in higher levels of chemicals that are thought to trigger inflammation. The opposite was true for the low-fat diet.

The authors reason that a high-carb, low-fat diet might benefit the gut due to the resistant starch present in white rice and bread.

“Given that dietary fibre intake did not differ among the three [diet] groups, it is possible that the favourable effects of the lower-fat diet in our study might be due to the increased amount of resistant starch which can, like dietary fibre, be fermented by the gut microbiota, with associated health benefits,” the paper reads.

More research is needed to prove causation and understand why a high-fat, low-carb diet impacts gut bacteria.

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