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How to look after your liver: Scrap detoxing, raw food and juice-cleansing

Eating too much of a good thing, “natural” or not, will eventually become toxic – even carrots.

Dr Giles Yeo takes on the detoxing, raw food and juice-cleansing movements.

If you’ve over-indulged in festive food and alcohol the past few weeks, you might be thinking about your over-worked liver and holiday weight gain – even considering a detox diet or juice cleanse, as promoted by any number of lissome, shiny-haired “wellness” bloggers and cookbook authors.

Dr Giles Yeo would tell you to hold that thought – actually, ditch it altogether. Not only is your diet probably doomed to failure, but that fruit-juice “cleanse” is likely to do your liver more harm than good.

Yeo has science on his side. The geneticist is based at Cambridge University’s Metabolic Research Laboratories, where he is director of genomics, with more than 20 years’ experience dedicated to researching obesity and the brain control of food intake. He describes his new book, Gene Eating, as an “anti-diet book” – devoted as it is to debunking claims made by many of the popular diet plans, such as “paleo” and “clean eating”. Instead, he places the obesity epidemic in perspective; asks if we can be “metabolically healthy without being skinny”; and ponders recent genetic breakthroughs that could usher in an era of personalised diets tailored to our genes.

The following extract from Gene Eating takes on the “cleanse and detox” movement, and explains what really keeps your liver running smoothly.

Dr Giles Yeo.
It’s one of the more underappreciated organs that keeps the body ticking. Our liver.


The liver plays a major role in carbohydrate, protein and lipid metabolism. For example, it converts glucose to glycogen when glucose levels are high, and converts glycogen back to glucose when glucose levels are low. It makes protein and it degrades protein. It is responsible for the synthesis of cholesterol, lipids and fatty acids. The liver also plays key roles in digestion through the production of bile, which is critical in the breakdown of fat, and in the storage of certain vitamins (A, D, B12 & K) and minerals (iron and copper). Crucially, our liver is responsible for the breakdown and excretion of many waste products. It is, in effect, a professional detox organ. The entire blood supply from our digestive tract and most other organs drains directly into the portal vein, which is piped straight into the liver. The liver then sorts through everything in the blood, storing or metabolising nutrients and working to eliminate toxins through a complex series of enzymatic processes. The first of these steps is to neutralise or alter the toxin. The next step is to take the altered toxin and alter it some more, often by adding another component to it such as a particular amino acid or sulphur. This renders the compound less harmful and often makes it water-soluble, thus it is able to be excreted from the system either in urine or bile.

A healthy functioning liver does this all of the time, whether you’re asleep or awake. It works harder after you’ve eaten, and after you’ve had a beer or a glass of wine. If you’ve had a few too many, the blood then needs to pass through the liver a few times before the alcohol is metabolised, during which time you will feel its effects. The liver is so effective in metabolising potential toxins that when drugs are being developed, the effective dose has to take into account the liver’s “drug metabolism” rate.

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The situation in which actual bona fide “detoxification” is needed is when someone is being treated for a dangerous level of a substance that is life-threatening. The term detox, for instance, is correctly used for the process of trying to remove drugs of abuse from your system; so going “cold turkey”. But that is a process where you stop taking something, and then let your body, mostly your liver, clear out the drugs or chemicals that are in the system. Equally, many of you might have participated in “dry January”, where you try and give your liver “a break” from all that festive bubbly and port. Once again, this is a completely legitimate process, because you are giving up alcohol for a month. So exclusion is the way to do “detox” because you are letting your liver get on with its professional role. There is no evidence that anything you eat can accelerate or enhance this process.  

The liver, together with your kidneys, intestines, lungs, lymphatic system and skin, work constantly to keep the body in a state of equilibrium and health. Virtually every cell in your body has mechanisms that are activated in the presence of toxins to protect itself and its neighbours.

The liver works harder after you’ve eaten, and after you’ve had a beer or a glass of wine.

One man’s meat is another’s toxin

So what exactly are these toxins that the liver is detoxing us from? The answer to this might surprise many. In the words of the 16th-century Swiss physician Paracelsus, “Only the dose makes the poison.” It is all about dose; most substances are fine in small amounts and almost everything becomes toxic at a high enough dose.

What constitutes a high dose very much depends on what the compound is, and the person taking it. Medicines, for instance, are what most of us would think of immediately when we discuss dose. We all know it is wise to take what the doctor tells you or what it says on the back of the pack; taking too much and overdosing on prescription drugs is simply not something most of us would intentionally do. Yet the same is true for nearly all substances, some with scary-sounding names, others seemingly benign. For example, metals like iron and magnesium are required by our bodies in small amounts, but rapidly become toxic at high levels.

Whatever you may think of pesticides, the levels you might find on a (non-organic) vegetable or fruit or nut are highly unlikely to kill you. Yet, ingesting even a small amount of the undiluted pesticide probably would. Botulinum toxin, commercially known as Botox, is a product of the bacteria Clostridium botulinum and is used (ill advisedly, I would suggest, although who am I to judge) as a cosmetic tool by some to reduce the visible signs of wrinkles. But, get the dose even slightly wrong, and it is one of the most dangerous toxins known to man. 

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The same too is true for all foods, including fruits and vegetables (before all of you begin throwing bananas at me, please hear me out). Carrots, for example, are clearly great for you, either raw or cooked or put in a soup, but yet if you eat too many, like a bin-bag worth (highly unlikely for most people), you would get poisoned by the beta-carotene, which gives carrots their orange colour. This is a condition known as beta carotenemia, where you essentially end up with a carrot-orange tinge to your skin. This is not unique to carrots; too much (but like wayyyyy too much) squash, pumpkins, sweet potatoes and other orange-coloured produce would have the same effect.

Another example is coconut water, which is refreshing and hydrating but has very high levels of potassium. There have been reported cases of people rushed to the hospital after suffering from fainting spells and abnormal heart rhythms due to hyperkalaemia (high blood potassium) from overdoing the coconut water. Higher potassium levels are also found in bananas and some vegetables, such as kale. Finally, broccoli and other members of the brassica family actually contain trace amounts of formaldehyde. So in principle, you could get formaldehyde poisoning by eating too much broccoli. Granted, you would have to eat a whole lot of bananas and drink quite a bit of coconut water or broccoli juice to end up being poisoned, but my point is that too much of a good thing, “natural” or not, will eventually become a bad thing, a toxic thing.

Natural sugar

At this point, many of you might be thinking that juicing doesn’t actually sound that bad. For one thing, fruit juices in particular taste fantastic; they are refreshing, sometimes they are zingy, they come in a huge assortment of colours and flavours, and all of them are sweet. The one thing you get a lot of in fruit juices is sugar. There is nearly as much sugar in a glass of orange juice (8g/100ml or 8%) and apple juice (10%) as there is in Coca-Cola (10.6%).

Surely the fact that the sugar in juice is “natural”, coming as it has from fruit, means it is better for you than the refined stuff added to soda? Absolutely not true. The vast majority of sugar in juice and in soda is sucrose, which is a disaccharide formed from one molecule of glucose and one molecule of fructose. So sucrose, when broken down becomes 50% glucose and 50% fructose. The sucrose added to soda might be refined, but it would have come from sugar cane or sugar beet, so is also “natural”.

How about sugar from honey or maple syrup or agave nectar? They are often marketed as better for you, or more curiously, as a “sugar-free” alternative. This is simply not true. They do, of course, taste different because one is in effect bee puke, another is tree sap and another concentrated cactus juice, so naturally each brings its own distinct flavour to different recipes. But they are sweet because of sugar.

In some countries, high fructose corn syrup is used to sweeten sodas and baked goods instead. High fructose corn syrup is made by enzymatically converting cornstarch (which would be mostly chains of glucose) to an approximately 50% glucose and 50% fructose mixture. Why not just use pure glucose? Because pure glucose, if you’ve ever tried it, tastes very odd and is almost unpalatable. The yummy flavour in sugar actually comes from the fructose portion. So in spite of the name, “high” fructose corn syrup contains as much fructose as sucrose. Some people don’t like the fact corn syrup is the product of an industrial process, and we can certainly debate the pros and cons of the increasing use of such products. But the incontrovertible and unequivocal fact of the matter is that sugar is sugar, whatever its source, wherever it comes from.

Is sugar bad for you? This will probably be an unpopular response, but the answer is that it entirely depends on how much you consume. At the risk of sounding like a broken record, it is a question of dose. When you eat an apple or an orange, you are taking in sugar. However, it probably takes five or six oranges to make a glass of orange juice. Would you ever eat six oranges in one sitting? Very unlikely. Yet you would give almost no thought to consuming six oranges worth of sugar in a single glass of juice during breakfast, which as I pointed out above, is no different from the amount of sugar you’d get from drinking a soda at breakfast.

Another problem is the delivery of sugar as a liquid. Sugar is calorically dense, and when dissolved into a liquid, you can suddenly deliver hundreds of calories into your system in literally seconds. When you eat anything, whether or not it is sweet, you have to first chew the food. As you do this, you begin to salivate, which your gastrointestinal tract senses, and as a result begins to prepare itself for nutrients to arrive, including secreting hormones and adjusting your metabolism. The hormones that are secreted when solid food is consumed are what make you eventually feel full and stop eating. When your calories are in the form of a sweet drink, however, they pass through the stomach into the small intestine and are very rapidly absorbed with no digestion. As no digestion has occurred, the release of hormones that make you feel full are delayed and, as a result, you end up eating more than you actually required. If you like sweet things, it is far better to eat them than it is to drink them.

In addition to the release of hormones that will eventually make you feel full if you actually eat fruit, there is the important benefit of consuming the fibre found in the fruit. Fibre plays a crucial role in gut health, both for motility and to nourish your gut bacteria. Additionally, the fibre reduces the caloric availability of the sugar in the fruit, which means you also get less sugar. The vast majority of the fibre found in fruit and in vegetables is lost during the juicing process, whether or not you use a cold-press or a centrifugal juicer.

Uncooked goose foie gras – literally “fat liver” in French.

When your liver is not working

As with most things in life, the importance of the liver is highlighted when, for one reason or another, it doesn’t work. My dad, together with his inability to metabolise lactose, cannot drink alcohol; like literally not a single drop. I remembered on the day I graduated from university, our department hosted a champagne drinks reception for the proud parents. My dad took a glass; all he did was sniff it, and the minute quantity of alcohol being aerosoled into his nose by the bubbles was enough to make him turn pink! I took the glass away from him because he was on photography duty that day to capture me on stage in my big moment – years of hard work in the making.

The reason for this is because he, like many other Chinese folk, has a deficiency in the enzymes that metabolise alcohol. These enzymes, alcohol dehydrogenase and acetaldehyde dehydrogenase, are localised to the liver. After having a drink, the blood carrying alcohol is filtered through the liver, where, if the enzymes are working, alcohol is then metabolised. If however, like in my dad, they are not, then the alcohol, even minute amounts of it, continues to circulate in the blood for a long time. My dad can end up being quite tipsy on even the smallest quantities of bubbly wine.

Then there are situations where your liver is actually physically damaged. Your liver plays a key role in metabolising lipids. However, when you have a number of highly fatty meals in a row, lipids can end up accumulating in your liver cells, resulting in a “fatty liver”. This is exactly what happens in foie gras, when the liver of a duck or goose is fattened by force-feeding corn. Foie gras literally means “fat liver” in French. Normally, your fatty liver is reversible with a change in diet, but it does kinda put me off my food, albeit fleetingly, if I think too hard about my liver turning from deep purple to light pink as it fills up with fat.

The problems begin when your liver stays fatty for too long because, in an increasing number of people, it is accompanied by inflammation, resulting in a situation referred to as “steatohepatitis” or fatty liver disease. At its most severe, this steatohepatitis can lead to liver cirrhosis, which is scarring that occurs in response to damage to the liver. Each time the liver is injured, it tries to repair itself, and in the process, scar tissue forms. As more and more scar tissue forms, it makes it difficult for the liver to function. 

Another way of getting fatty liver disease is through alcohol abuse. What does alcohol have to do with a fatty liver, you might ask? Well, the liver is where alcohol is metabolised; as a consequence, abuse of alcohol will eventually damage the liver. Because another key role of the liver is lipid metabolism, if your liver is irreparably damaged by alcohol, it is then unable to metabolise lipids effectively, resulting in accumulation of lipids, fatty liver disease, leading, in some, to liver cirrhosis. Two different causes of liver damage, but with the same result.

A little-known fact is that sugar can also play a role in the health, or not, of the liver. Sucrose, as I mentioned, is broken down to glucose and fructose. As long as you are not diabetic, glucose is almost immediately taken up by your skeletal muscles and your fat after a meal, in response to insulin. Fructose, however, ends up in the liver, where if not used immediately, it is actually converted to fat. So if you are knocking back serious amounts of sugar, which is what you would effectively be doing during a “fruit juice cleanse”, you are actually putting your liver under pressure. Ironic, given that one of the juice-cleanse claims is that it is giving your liver a break. Nothing could be further from the truth.

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One of the overt signs that all is not right with the liver is jaundice, which many of us would recognise as a yellowing of the skin and eyes. When red blood cells have completed their life span of approximately 120 days, they have to be broken down and excreted, and this is one of the primary roles of the liver. The oxygen-carrying component of red blood cells is called haemoglobin, which is also what gives the cells, and hence blood, its deep red colour. One of the breakdown products of haemoglobin is bilirubin, which is yellowish in colour and becomes a key part of bile. Bile is produced by the liver and secreted into the small intestine, where it aids the digestion of lipids. Some bilirubin is also excreted via urine. In fact, bilirubin is actually what gives faeces and urine their distinct colour. When the liver is not working however, instead of being shunted to bile, the yellow bilirubin stays in the circulation, resulting in jaundice. Jaundice is therefore not a disease per se, but a symptom of a liver that is not working well.

In fact, with more than 500 known functions, the role of the liver is nigh on impossible to replicate. For instance, while you can undergo kidney dialysis when your kidney fails, there is, certainly at time of writing, no “liver dialysis” procedure yet available. While the liver is famously able to regenerate, it can only do so from regions that are not cirrhotic, so when too much cirrhosis has occurred, the liver then begins to fail. There is currently no way to compensate for the absence of liver function in the long-term. When this happens, the only option remaining is a liver transplant. Liver failure is, tragically, incompatible with life. 

The bottom line is, there is currently no scientific evidence to support the supposed benefits of juice cleansing or of detox. The marketing of this sector plays into the misconception that cleansing and detoxing are vital to the maintenance of bodily functions, therefore it would be in our best interest to undertake one or we risk developing chronic and terminal illnesses. The truth is, none of the purveyors of “detox” products can tell you what we are supposed to be detoxing from, let alone show that using their product will reduce said unknown yet potentially deadly toxin. To have a well-functioning liver you simply have to eat healthy foods and limit consumption of substances, such as alcohol or large amounts of fructose that cause it to work harder. Excessive consumption of any food can and will contribute to an increased load on the liver.

Juice cleanses are being sold as a philosophy of life; those who undertake them will emerge cleaner, more balanced, free of stress – ultimately a better version of themselves, superior to both their previous selves and uncleansed counterparts. This idea is not new. Cleansing or fasting practices are found in every major religion, to purify both body and soul.

Generally speaking however, for most people, detox and cleanse are typically confined to the month of January, and tends to mean drinking a little less, eating more healthily and getting a reasonable amount of exercise. Of course you will feel better! But you do not need any special products and you do not need to spend any money to do this. The evidence-backed approach, boring though it is, is that a healthy, well-balanced diet based on national guidelines is still the best “cleanse and detox” available. 

Edited extract from Gene Eating: The Science of Obesity and the Truth about Diets by University of Cambridge geneticist Dr Giles Yeo (Hachette, $38).

Almond trees in California, where 80% of the world’s crop is grown. Photo/Thinkstock

Raw Nuttiness: Is raw food really better?

Raw foodies define “raw food” as anything that has not been refined, canned or chemically processed, and has not been heated above 48°C. They claim that heating your food above 48°C destroys some of the natural enzymes in food, so the body overworks itself by having to produce more of its own enzymes, exhausting its energy.

There is much to pick apart in this claim. Cooking your food will not only destroy some of the natural enzymes, it will destroy pretty much all of the enzymes in the food. Crucially, however, so will the acid in your stomach. Whatever hardy enzymes and other proteins that do survive that acidic cauldron of the stomach will then be fully digested in the small intestines before being absorbed into our system.

When we consume another organism, everything is broken down into their basic building blocks, and reassembled in each cell according to the instructions on our own human DNA. Most of us, I hope, understand that if you eat an antelope, it won’t make you run faster, nor would having a kangaroo steak make you jump any higher. Likewise, we do not eat a chicken or salmon or for that matter a broccoli enzyme or protein complex, and have that very same broccoli enzyme or salmon protein suddenly functioning in us. That is simply not how biology works.

Another claim is that if you cook your food above 57°C (these are some very specific temperatures), it destroys heat-sensitive nutrients. This is of course true; the classic example being vitamin C, which is famously heat-sensitive. We get around that by eating much of our fruit, and some of our vegetables, which are of course rich in vitamin C, raw. This is undoubtedly something we don’t do enough of and is to be encouraged. Equally, however, cooking many other foods makes nutrients more available to us. For example, cooking carrots and tomatoes makes it easier for our bodies to benefit from their protective antioxidants, and cooking sweet corn allows us to access the niacin more easily. The challenge for anyone on a raw food diet is getting enough protein, vitamin B12 and iron, as these nutrients are typically found in foods that are best heated above 57°C, including meat, fish, eggs and grains. Cooking, of course, also kills most parasites that might be present in the food, which surely is a good thing…. otherwise you might end up losing weight for entirely the wrong reason!

Goji berries, blueberries, kale, avocado, wheatgrass, cinnamon, quinoa and garlic. Aside from being members of the plant kingdom, what do all of these foods have in common? They have achieved the status of “superfoods”. These foods are of course all healthy; some like cinnamon may very well have medicinal qualities, and garlic has the added advantage of being able to repel vampires. But are they “super” in any way? 

Since the beginning of humankind, eating some foods has been thought to slow down ageing, or lift depression, or boost our physical ability, make us cleverer, heal us and stop pain. Some of these, such as the use of willow leaf extract to relieve pain and lower fevers, genuinely do work, as the chemical salicylate found in the extract is a precursor to aspirin. Others, however, are simply old wives’ tales or witch doctors’ cures with no evidence of working. To my mind, superfoods are their modern equivalent, each having some supposed magical health property, with many of us, for instance, desperate to believe that eating a single fruit or vegetable containing a certain antioxidant will zap a diseased or cancerous cell.

While the superfoods I have listed (and there are many more available that I shan’t be listing here) are indeed healthy, and each contain some genuinely important nutrients (antioxidants in berries) or healthy fats (avocados), today eating enough is suddenly not enough. Eating MORE is better than eating enough. If something is good for you, surely more of a good thing is better? Not true. There is a healthy and a toxic dose for most foods.

Remember: “Only the dose makes the poison.”


What exactly is cold-pressed juice?

Instead of using a centrifugal juicer (the kind you would have in your kitchen), which employs a blade that can heat up, cold pressing essentially squashes and squeezes the fruit and veg to remove their juices.

The process is carried out in a giant fridge at 4°C that, so they say, ensures the juice retains its highest possible nutritional density and “enzymatic activity”, while limiting oxidisation. It also allows the juice to stay consumable for up to three days after pressing and so be bottled and sold in bright-coloured shops by tall, lanky women who used to model and young men with six-pack abs.

Some companies high-pressure pasteurise the bottled juice, which extends the shelf life to months. However, this process is frowned upon by the true raw-cold-pressed-green juice aficionados. Most juice companies are adamant about cold-pressing and tout it as the optimal process for extracting juice (which has the added benefit of allowing them to charge £6 [$11+] for a 500ml bottle – quite a lot of money). 

A “juice cleanse” programme normally involves forgoing all solid foods, and instead ingesting around three litres of juice, containing 800-1200 calories a day, for a period ranging from one to seven days (or longer). [Programmes in the UK cost around £40, close to $75 a day.]

This article was first published in the February 2019 issue of North & South.

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