Fermented foods have become popular in recent years, partly due to their perceived health benefits.
For instance, there is some evidence eating or drinking fermented foods can improve blood glucose control in people with diabetes. They can lower blood lipid (fats) levels and blood pressure in people with diabetes or obesity. Fermented foods can also improve diarrhoea symptoms.
But can they help you lose weight, as a recent study suggests? Let's look at the evidence.
Remind me, what are fermented foods?
Fermented foods are ones prepared when microbes (bacteria and/or yeast) ferment (or digest) food components to form new foods. Examples include yoghurt, cheese, kefir, kombucha, wine, beer, sauerkraut and kimchi.
As a result of fermentation, the food becomes acidic, extending its shelf life (food-spoilage microbes are less likely to grow under these conditions). This makes fermentation one of the earliest forms of food processing.
Fermentation also leads to new nutrients being made. Beneficial microbes (probiotics) digest nutrients and components in the food to produce new bioactive components (postbiotics). These postbiotics are thought to contribute to the health benefits of the fermented foods, alongside the health benefits of the bacteria themselves.
What does the evidence say?
A study published last week has provided some preliminary evidence eating kimchi – the popular Korean fermented food – is associated with a lower risk of obesity in some instances. But there were mixed results.
The South Korean study involved 115,726 men and women aged 40-69 who reported how much kimchi they'd eaten over the previous year. The study was funded by the World Institute of Kimchi, which specialises in researching the country's national dish.
Eating one to three servings of any type of kimchi a day was associated with a lower risk of obesity in men.
Men who ate more than three serves a day of cabbage kimchi (baechu) were less likely to have obesity and abdominal obesity (excess fat deposits around their middle). And women who ate two to three serves a day of baechu were less likely to have obesity and abdominal obesity.
Eating more radish kimchi (kkakdugi) was associated with less abdominal obesity in both men and women.
However, people who ate five or more serves of any type of kimchi weighed more, had a larger waist sizes and were more likely to be obese.
The study had limitations. The authors acknowledged the questionnaire they used may make it difficult to say exactly how much kimchi people actually ate.
The study also relied on people to report past eating habits. This may make it hard for them to accurately recall what they ate.
This study design can also only tell us if something is linked (kimchi and obesity), not if one thing causes another (if kimchi causes weight loss). So it is important to look at experimental studies where researchers make changes to people's diets then look at the results.
How about evidence from experimental trials?
There have been several experimental studies looking at how much weight people lose after eating various types of fermented foods. Other studies looked at markers or measures of appetite, but not weight loss.
One study showed the stomach of men who drank 1.4 litres of fermented milk during a meal took longer to empty (compared to those who drank the same quantity of whole milk). This is related to feeling fuller for longer, potentially having less appetite for more food.
Another study showed drinking 200 millilitres of kefir (a small glass) reduced participants' appetite after the meal, but only when the meal contained quickly-digested foods likely to make blood glucose levels rise rapidly. This study did not measure changes in weight.
Another study looked at Indonesian young women with obesity. Eating tempeh (a fermented soybean product) led to changes in an appetite hormone. But this did not impact their appetite or whether they felt full. Weight was not measured in this study.
A study in South Korea asked people to eat about 70g a day of chungkookjang (fermented soybean). There were improvements in some measures of obesity, including percentage body fat, lean body mass, waist-to-hip ratio and waist circumference in women. However there were no changes in weight for men or women.
A systematic review of all studies that looked at the impact of fermented foods on satiety (feeling full) showed no effect.
What should I do?
The evidence so far is very weak to support or recommend fermented foods for weight loss. These experimental studies have been short in length, and many did not report weight changes.
To date, most of the studies have used different fermented foods, so it is difficult to generalise across them all.
Nevertheless, fermented foods are still useful as part of a healthy, varied and balanced diet, particularly if you enjoy them. They are rich in healthy bacteria, and nutrients.
Are there downsides?
Some fermented foods, such as kimchi and sauerkraut, have added salt. The latest kimchi study said the average amount of kimchi South Koreans eat provides about 490mg of salt a day. For an Australian, this would represent about 50% of the suggested dietary target for optimal health.
Eating too much salt increases your risk of high blood pressure, heart disease and stroke.
Evangeline Mantzioris, Program Director of Nutrition and Food Sciences, Accredited Practising Dietitian, University of South Australia
This article is republished from The Conversation under a Creative Commons license. Read the original article.
