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.

Everyone seems to have a different opinion when it comes to how often towels and bed sheets should be washed. While many people might wonder whether days or weeks is best, in one survey from the United Kingdom, almost half of single men reported not washing their sheets for up to four months at a time.

It’s fairly clear that four months is too long to leave it, but what is the ideal frequency?

Bed linen and towels are quite different and so should be washed at different intervals. While every week or two will generally suffice for sheets, towels are best washed every few days.

Anyway, who doesn’t love the feeling of a fresh set of sheets or the smell of a newly laundered towel?

Why you should wash towels more often

When you dry yourself, you deposit thousands of skin cells and millions of microbes onto the towel. And because you use your towel to dry yourself after a shower or bath, your towel is regularly damp.

You also deposit a hefty amount of dead skin, microbes, sweat and oils onto your sheets every night. But unless you’re a prolific night sweater, your bedding doesn’t get wet after a night’s sleep.

Towels are also made of a thicker material than sheets and therefore tend to stay damp for longer.

So what is it about the dampness that causes a problem? Wet towels are a breeding ground for bacteria and moulds. Moulds especially love damp environments. Although mould won’t necessarily be visible (you would need significant growth to be able to see it) this can lead to an unpleasant smell.

As well as odours, exposure to these microbes in your towels and sheets can cause asthma, allergic skin irritations, or other skin infections.

So what’s the ideal frequency?

For bedding, it really depends on factors such as whether you have a bath or shower just before going to bed, or if you fall into bed after a long, sweaty day and have your shower in the morning. You will need to wash your sheets more regularly in the latter case. As a rule of thumb, once a week or every two weeks should be fine.

Towels should ideally be washed more regularly – perhaps every few days – while your facecloth should be cleaned after every use. Because it gets completely wet, it will be wet for a longer time, and retain more skin cells and microbes.

Wash your towels at a high temperature (for example, 65°C) as that will kill many microbes. If you are conscious of saving energy, you can use a lower temperature and add a cup of vinegar to the wash. The vinegar will kill microbes and prevent bad smells from developing.

Clean your washing machine regularly and dry the fold in the rubber after every wash, as this is another place microbes like to grow.

Smelly towels

What if you regularly wash your towels, but they still smell bad? One of the reasons for this pong could be that you’ve left them in the washing machine too long after the wash. Especially if it was a warm wash cycle, the time they’re warm and damp will allow microbes to happily grow. Under lab conditions the number of these bacteria can double every 30 minutes.

It’s important to hang your towel out to dry after use and not to leave towels in the washing machine after the cycle has finished. If possible, hang your towels and bedding out in the sun. That will dry them quickly and thoroughly and will foster that lovely fresh, clean cotton smell. Using a dryer is a good alternative if the weather is bad, but outdoors in the sun is always better if possible.

Also, even if your towel is going to be washed, don’t throw a wet towel into the laundry basket, as the damp, dirty towel will be an ideal place for microbes to breed. By the time you get to doing your washing, the towel and the other laundry around it may have acquired a bad smell. And it can be difficult to get your towels smelling fresh again.

What about ‘self-cleaning’ sheets and towels?

Some companies sell “quick-dry” towels or “self-cleaning” towels and bedding. Quick-dry towels are made from synthetic materials that are weaved in a way to allow them to dry quickly. This would help prevent the growth of microbes and the bad smells that develop when towels are damp for long periods of time.

But the notion of self-cleaning products is more complicated. Most of these products contain nanosilver or copper, antibacterial metals that kill micro-organisms. The antibacterial compounds will stop the growth of bacteria and can be useful to limit smells and reduce the frequency with which you need to clean your sheets and towels.

However, they’re not going to remove dirt like oils, skin flakes and sweat. So as much as I would love the idea of sheets and towels that clean themselves, that’s not exactly what happens.

Also, excessive use of antimicrobials such as nanosilver can lead to microbes becoming resistant to them.

Rietie Venter, Associate professor, Clinical and Health Sciences, University of South Australia

This article is republished from The Conversation under a Creative Commons license. Read the original article.