Eating liver is less popular now than it was a few decades ago, although it has enjoyed a recent resurgence1. It is a very cheap source of nutrients, firstly because demand for it is not that high and secondly, because it is packed full of more nutrients, than virtually any other food you can think of.
Why is liver so full of good nutrition?
The liver is the 2nd largest organ in the human body (after the skin), and is responsible for numerous vital functions. Many of these functions result in a concentration of vital nutrients being present in the liver. The nutrients present and their origin is shown below2:
- 56% water. The liver creates most of the lymph for our body. As such it is full of water. It also contains large amounts of blood, a fact that can easily be understood if you ever cook with liver.
- 26% protein. The liver is responsible for making a lot of the proteins our body needs. It synthesizes the albumin transport protein and 12 amino acids that are used to form many types of protein for use in the body.
- 5.0% saturated fat. The liver makes fat from excess carbohydrate. It can then break down the fat to provide a ready source of slow burning energy for the body.
- 3.8% carbohydrate. The liver stores some of the excess sugar and starch in our diet as glycogen. This can be broken down to supply blood sugar to keep our brain ticking over.
- 2.5% mono unsaturated fat.
- 1.7% w6 fatty acids in the form of arachidonic acid and linoleic acid.
- 0.5% cholesterol. The liver is known for its cholesterol content. However, our liver is good at adjusting for cholesterol in the diet. It does this by at least two mechanisms: 1) converting excess cholesterol into bile acids that it dumps in our intestines or gall bladder and 2) slowing down the formation of cholesterol in the liver. Yes the liver makes cholesterol as well as a host of other substances that our body needs to survive.
- 0.2% w3 fatty acids as linolenic acid and its health promoting derivatives EPA and DHA. Pork liver is shown as containing appreciably more EPA and DHA, than lamb's liver. I suspect this is more to do with what was going on in the body of the animal when slaughtered, than any intrinsic difference between pigs and sheep. In fact EPA and DHA are synthesized in the liver of most mammals, most of which is then utilised within the brain and central nervous system.
Micronutrients contained in 100g of liver
- Vitamin B12: 3 - 10 times the daily requirement. However unlike vitamin A below, B12 is not toxic in excess.
- Vitamin A: 3 - 5 times the daily minimum requirement. In animal such as polar bears the concentration of vitamin A is so strong it is toxic to humans and many polar explorers have died from consuming polar bear liver3. Eating liver every day would be unwise, especially for pregnant women. There is much debate about the safety of vitamin A supplements and indeed, liver, with some researchers suggesting that we should consume less than we do. However, I find a recent hypothesis that vitamin A is safer when levels of vitamin D are high quite convincing4. Liver does not provide much vitamin D, whereas sunlight, fish oils and high strength supplements do. I would suggest that you eat liver no more than twice a week unless you are getting plenty of sun or are supplementing more than 2000IUs of vitamin D per day.
- Vitamin B: From 0.5 - 3 times the daily requirement. The liver is a great source of B vitamins that provide energy, and can improve mental health, cardiovascular health and hormonal health.
- Vitamin D: Trace amounts. The liver converts vitamin D produced in the skin in response to sunlight, to a more active form known as 25(OH)D. This is then further converted to 1,25(OH)D by the kidneys. The liver contains only small amounts of vitamin D.
- Vitamin K: Trace amounts. The liver contains only small amounts of vitamin K.
- Copper: Highly variable amounts ranging from a 1/3rd of the daily requirement to a whopping 7 times the daily requirement. Too much copper can lead to problems, but the amounts in liver should not give rise to concern.
- Selenium: Approximately the daily requirement. Selenium is used primarily as an anti-oxidant in the body. It is considered to boost the immune system and potentially protect against cancer.
- Iron: Approximately the daily requirement. Liver is a great source of iron, which makes it a great food for non-pregnant women.
- Zinc: 1/2 the daily requirement.
|Pan Fried Liver|
|% of RDA in 100g portion|
Buying and cooking liver.
Liver is best bought from a butchers, who generally have better quality livers than the supermarkets. If your slices are cut from a whole liver in front of you then that suggests they have not been hanging about too long. Some pieces of liver contain more tubules than others and this can affect the taste. The smoother the appearence the better in my experience.
Liver and onions is a popular dish that comprises the following (for 2 people):
- 200g/1lb lambs’ liver, sliced and fully thawed if frozen
- 10g butter
- 1 tbsp olive oil
- 1 tbsp plain flour
- 4 rashers of bacon
- 1 sliced onion
- 250ml boiled water
- 2 chopped tomatos
- Rinse the liver under cold water and drain on kitchen paper. Melt the butter with the oil in a large non-stick frying pan.
- Put the tablespoon of flour in a bowl and season with freshly ground black pepper.
- Coat the liver in the seasoned flour, then fry each slice in the pan for 2-3 minutes on each side until lightly browned (sealed).
- Add the sliced onion and cook for a minute or so, stirring to separate the layers.
- Add the bacon rashers to the pan, stirring from time to time until the onion is pale golden-brown and the bacon is beginning to crisp.
- Add the chopped tomatoes.
- Serve the liver and bacon with some freshly cooked greens. Add in mashed potato if you are hungry.
Liver is a cheap and tasty treat, and one of the most nutritious foods that you will find. It is a potent source of vitamins A, B, selenium, copper, iron and zinc. Many people are marginally deficient in some or all of these nutrients, and so a regular portion of liver makes a lot of sense. It is best eaten occasionally, perhaps once a week or fortnight. If you don't get a lot of sunlight exposure, or are not taking a high strength supplement of vitamin D, then once per week is probably enough. The reason is, that excess vitamin A is associated with reduced bone density. Vitamins D and K2 are thought to balance out this effect to some extent.
1) http://www.express.co.uk/posts/view/200356/Offal-sales-soaring Offal becoming more popular.
2) http://nutritiondata.self.com/facts/lamb-veal-and-game-products/4670/2 Nutrient composition of lamb's liver.
3) http://science.howstuffworks.com/environmental/life/zoology/mammals/eat-polar-bear-liver.htm Don't eat polar bear liver.
4) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2715292/ Vitamin A not so bad as we think.