Sugar, Alcohol and Your Liver

In my last blog I explained why fatty liver has a new name, MASLD, and why it has far more to do with metabolic health than most people expect. The natural next question is one I hear in clinic all the time: "So what is it in my diet that is doing the damage?"

Some people are convinced it must be sugar. Others quietly worry about the wine. And a quick search online will tell you that what you really need is a liver detox. The honest answer is more nuanced than any of those. No single food is responsible, but some things clearly matter more than others. Let's look at what the evidence shows.

Is Sugar the Problem?
Sugary drinks have the most consistent evidence against them. A 2019 analysis pooled 12 studies involving more than 35,000 people and found that those who drank sugar-sweetened drinks had 39% higher odds of having a fatty liver. The risk rose with the amount: it was 14% higher in people having less than one drink a week, 26% higher at one to six a week, and 53% higher at seven or more.

Studies like these can only show a link, so trials are helpful here. In one six-month trial, 47 adults living with overweight drank a litre a day of either regular cola, milk, diet cola or water. Liver fat rose markedly more in the regular cola group than in any of the others, as did the fat stored around the abdominal organs.

Why drinks in particular? Sugar in liquid form is very easy to consume in large amounts and does little to fill us up. As I described in my last blog, the liver can turn surplus carbohydrate into new fat, and sugary drinks seem to be a particularly efficient way of encouraging it to do so.

Does That Mean All Sugar Is Bad for the Liver?
Not quite, and this is where the headlines tend to go wrong. A meta-analysis of 13 controlled feeding trials in healthy volunteers looked specifically at fructose, the sugar most often blamed. When fructose simply replaced other carbohydrates and total calories stayed the same, there was no effect on liver fat. When it was added on top of the diet as extra calories, in very large amounts, liver fat went up. The authors concluded that the effect may owe more to the excess energy than to the fructose itself.

In other words, context matters. The NHS advises adults to have no more than 30g of free sugars a day, which is roughly seven sugar cubes. Free sugars are those added to food and drinks, plus the sugars in honey, syrups, fruit juices and smoothies. The sugar found naturally in whole fruit, vegetables and milk does not count, and the NHS is clear that we do not need to cut down on these. So, there is no need to fear a piece of fruit. Juice and smoothies are a different matter, and the advice is to keep these to no more than 150ml a day.

The Fat That Surprises People
Sugar gets most of the attention, but saturated fat deserves some too. In a 2018 trial, 38 adults living with overweight were given an extra 1,000 calories a day for three weeks. The extra calories came from saturated fat, unsaturated fat or simple sugars. Liver fat rose in all three groups, but not equally: by 55% with saturated fat, 33% with sugars and 15% with unsaturated fat.

This was a small, short study in which people were deliberately overfed, so it does not tell us what happens on a balanced diet. It does suggest that the type of fat matters to the liver as well as to the heart. The NHS recommends no more than 20g of saturated fat a day for women and 30g for men.

Where Does Alcohol Fit In?

As I mentioned in my last blog, the new terminology recognises that metabolic health and alcohol are not an either/or. Many people have a bit of both, and the evidence suggests that the two do more than simply add together.

A Scottish study published in the BMJ followed more than 9,500 men for a median of 29 years. Among men drinking 15 or more units a week, deaths from liver disease were around three times higher in those of a healthy weight, seven times higher in those who were overweight and almost 19 times higher in those living with obesity, compared with healthy-weight men who did not drink. The researchers concluded that weight and alcohol amplify one another. The study only included men and began in the 1960s, but the pattern is striking.

What about lighter drinking? A Finnish study of more than 8,000 adults with a fatty liver found that 10 to 19g of alcohol a day, roughly one to two and a half UK units, was associated with double the risk of advanced liver disease compared with lifelong non-drinkers. The same study found fewer cardiovascular events among drinkers who had never smoked, which shows how difficult alcohol research can be to interpret. For the liver itself, though, the direction was consistent: the more alcohol, the higher the risk.

So, what does the guidance say? The NHS advises men and women not to regularly drink more than 14 units a week, spread over three or more days. For reference, a 175ml glass of 12% wine is 2.1 units and a 750ml bottle of 13.5% wine is 10 units. NICE asks clinicians to explain the importance of staying within these limits to people with MASLD.

Liver UK notes that if you have MASLD, drinking alcohol can make liver damage worse. It suggests staying within 14 units with two to three alcohol-free days each week, and stopping completely if you have advanced scarring or cirrhosis. European guidelines go a little further and say that people with a fatty liver should be discouraged from drinking alcohol at all.

My reading of this is that 14 units is an upper limit, not a target, and that for liver health less is better. If you have been diagnosed with MASLD, your GP or liver specialist is the right person to advise on what is appropriate for you.

The Bigger Picture
When you put these studies side by side, a pattern emerges. Excess energy matters, whatever its source. Sugary drinks and saturated fat appear to be the least liver-friendly ways of taking in that excess. Alcohol adds to the load, particularly alongside excess weight.

This is why guidelines focus on the overall pattern of eating, not on single nutrients. European guidelines recommend improving diet quality along the lines of a Mediterranean-style pattern, limiting ultra-processed foods that are rich in sugars and saturated fat, and avoiding sugar-sweetened drinks. They also recommend regular physical activity to reduce liver fat.

Body composition is part of the picture too. For people living with overweight, the same guidelines set out targets: a sustained weight loss of 5% or more to reduce liver fat, 7 to 10% to improve inflammation, and 10% or more to improve scarring. For people of a healthy weight who have MASLD, diet and exercise are still recommended to reduce liver fat.

What About a Liver Detox?
It would be lovely if a tea, a juice cleanse or a capsule could undo all of this, but the evidence is simply not there! Liver UK states that no complementary or alternative medicines have been shown to treat or prevent MASLD, and that they can sometimes harm the liver. 

I have written before about why detox diets don't work, and the liver is a very good example. If you have a liver condition, it is always worth talking to your doctor before starting any supplement.

So, What Actually Matters?
Not one villain, but a handful of everyday habits: how often sugary drinks feature, how much saturated fat and ultra-processed food is in the mix, how much alcohol you drink, and whether your overall pattern of eating and moving is supporting your metabolic health. None of this requires perfection, and none of it requires a detox. In my next blog, I will turn all of this into practical top tips.

Need Some Support?
If you have been told you have MASLD, or you are concerned about your liver or your drinking, your GP should always be your first port of call. Alongside that medical care, personalised nutrition and lifestyle support can help you turn general healthy-eating advice into realistic changes that suit your life. Why not book in a free call?