Liver isn't just something that you eat (although that's important too, and you can read about it here). It’s also something that you have, and your own liver is definitely an organ you want to take care of: it's responsible for crucial functions like cholesterol synthesis, detoxification, and fat metabolism. Without a healthy liver, none of us would last very long, so learn how to keep yours humming along smoothly.
One way of doing this is to think about problems you’d like to avoid. There are a few different types of liver problems:
- Alcoholic hepatitis: fat deposits on the liver and liver breakdown caused, as the name implies, by excessive alcohol consumption
- Non-alcoholic fatty liver disease (NAFLD): accumulation of fat deposits on the liver in people who don’t drink.
- Non-alcoholic steatohepatitis (NASH): a more severe form of NAFLD.
- Autoimmune hepatitis: liver inflammation caused by an autoimmune attack on liver cells.
Liver problems don’t get a lot of press, except as an occasional footnote on the complications of obesity or alcoholism, but that’s not because they don’t exist. This paper estimates the prevalence of NAFLD alone at 20-30% in developed countries! In the overweight and obese, rates are even higher. But these patients often fly under the radar because subclinical liver problems develop slowly and often show no symptoms until the disease is very far advanced.
The implication of this is that even if you don’t notice anything wrong, you might still be having liver trouble on the inside. So what causes all these inflammatory conditions, and how can diet affect them?
How does Fat Get in the Liver?
Fat can accumulate on the liver from 3 different sources:
- Release of fatty acids from body fat deposits
- Dietary fat that “sticks” to the liver
- Fat created in the liver itself (de novo lipogenesis)
Today, most scientists agree on a “two-hit” theory of liver disease.
First hit: insulin resistance leading to de novo lipogenesis (synthesis of fat in the liver), fat released from body fat deposits, and other metabolic problems cause fat accumulation in and around the liver (NAFLD). This stage can last for years and is often asymptomatic.
Second hit: a perfect storm of inflammation, oxidative stress, and other factors causes permanent damage known as NASH and potentially progressing to cirrhosis.
So what does diet have to do with any of this?
Diet and Liver Disease: Insulin
Insulin, the hormone needed to digest carbohydrates and use them for energy, has a very important effect on liver health. A quick review of insulin: it’s a hormone that transfers glucose (carbs) from your food into your muscles, where it’s used for energy. In healthy people, this process causes a brief spike in insulin levels after eating a meal containing carbohydrates, but in people with metabolic problems, the story looks a little different. To put it very briefly, eating a metabolically inappropriate amount of carbohydrates (too many or too few) can make the muscles insulin resistant: they no longer open the door when insulin comes knocking with the carbs. The carbs get sent to the liver and stored as fat, and blood levels of insulin stay high.
Basically, insulin resistance is a physiological inability to handle eating carbs. And although it’s not totally clear which one is the cause and which one is the effect, insulin resistance and NAFLD/NASH go hand in hand. This study even described NAFLD as “the hepatic [liver-related] manifestation of the metabolic syndrome.” Patients with non-alcoholic liver problems are usually also insulin resistant if not outright diabetic, and often overweight as well (although not always: thin people can be insulin resistant too!).
Excess Carbs and Liver Problems
This study provided fairly dramatic proof of the theory that excess carbohydrates are important in the accumulation of liver fat: after 3 weeks of carbohydrate overfeeding (1000 calories/day of simple sugars), subjects’ weight increased only 2%, but their liver fat increased by 27%.
In this study, a very high-carb diet (75% of calories from carbs) elevated plasma triglycerides and decreased fat oxidation compared to a moderate-fat, moderate-carb (40% fat, 45% carbs) diet. In other words, the high-carb diet made the subjects store fat, rather than burning it. The study was a very short-term intervention (only 3 days), so it may not be relevant in the long term, but it’s interesting nonetheless.
Is Very Low-Carb Better?
This might make you think that a ketogenic diet is the best possible remedy for liver problems: get rid of the carbs, and the liver fat will follow. This study seems to support that: a ketogenic diet had dramatic results on fatty liver (93% of patients improved, and 21% went into complete remission), but considering that it was a tiny study with only 14 subjects, it’s hard to draw solid conclusions. And there’s also some evidence that ketosis might not be the best idea:
- A lot of fascinating studies on mice have found that long-term ketosis is actually quite stressful to the liver, although it’s not completely clear whether this applies to humans (since, for example, inducing ketosis in mice requires restricting protein as well as carbs).
- It’s very plausible that ketosis is overkill: moderate-carb diets without ketogenic levels of restriction can be very effective for NAFLD/NASH. For example, in this study, subjects got either 60% carbs/25% fat or 40% carbs/45% fat; at the end of the study period, the hormonal benefit was noticeably greater for the lower-carb group.
On the whole, the evidence seems to support a low- to moderate-carb diet, with potential for ketosis to be even better. But as usual, more research is needed before anyone has conclusive proof one way or another.
Diet and Liver Disease: Fructose
A very misunderstood carbohydrate when it comes to fatty liver disease is fructose. Fructose is the carbohydrate found primarily in fruit and table sugar. Food that tastes “starchy” (like potatoes, rice, or bread) has carbs primarily from glucose, while food that tastes “sweet” (like fruit) has a substantial amount of fructose.
Unlike the starchy carbs found in grains and tubers, fructose does not get channeled by insulin into the muscles. Instead, it’s sent straight to the liver, making it much easier to turn into fat instead of store in the muscles.
This makes fructose a prime suspect for fatty liver disease – and there are two types of evidence that seem to support this. First of all, high fructose intake in humans is associated with greater rates of NAFLD. Second, evidence in mice and rats seems to agree: an easy way to make a mouse’s liver very, very sick is to feed it a lot of fructose.
Is Fructose Really That Bad?
But the mouse studies are a perfect example of why animal research isn’t always applicable to humans. These mice are often eating over half their daily calories from fructose: that’s a level of sugar consumption that very few humans ever reach. As for the association between fructose intake in humans and NAFLD? That’s simple: high fructose intake = high consumption of soft drinks and candy = calorie and carbohydrate surplus (often with an accompanying micronutrient deficiency). Carbohydrate excess from any source will be dangerous to the liver, but fructose specifically isn’t any worse than anything else.
We know this because, in controlled human trials, fructose only has this effect when it’s eaten as part of a calorie surplus. In this study, for example the researchers compared a high-fructose and a high-glucose diet. At an appropriate calorie level, neither diet was particularly bad. At a caloric excess, they were both dangerous to the liver, but to approximately the same degree. There’s nothing specifically bad about fructose that’s different from the problems with high carb intake overall or calorie intake that exceeds the body’s energy requirements.
Another reason to suspect the fructose-NAFLD link is that fructose only seems to harm mice when they’re also deficient in another vital nutrient, choline (more on this below). Since a Paleo diet is full of choline almost by default, fructose is less of an issue.
For people concerned about their liver, this means there’s no reason to avoid fructose from whole foods like fruit. Apples and oranges will not give you liver problems. Coke, on the other hand, is a prime suspect, because the nature of sugar-sweetened drinks is that they’re very easy to overconsume without noticing it. So steer clear of sugar in a can, but don’t worry about the fruit salad.
Diet and Liver Disease: Fats
As you might expect from the name, fatty liver disease is strongly influenced by dietary fat. But don’t rush out to throw away your butter just yet, because the different types of fat all have different effects. The literature on NAFLD likes to demonize “high-fat” diets, without considering that the different types of fats have demonstrably different effects on liver health and metabolic function, and talking about a “high-fat” diet is uselessly imprecise.
There’s a lot of survey data that connects dietary saturated fat to fatty liver disease. But most of it is very lazy science: researchers look at the data about what people say they eat, notice that people who admit to eating more saturated fat also tend to have higher rates of liver disease, and conclude that the fat is to blame. But this is a classic case of the problems with epidemiological research. People who eat saturated fat today are mostly people who just don’t care about their health – they also smoke, drink, eat junk food, and don’t exercise. It’s impossible to just look at their fat intake alone and conclude that the fat is responsible for the liver disease.
What’s more, there’s actually evidence in both humans and animals that saturated fat does not cause fat accumulation in the liver in the absence of sugar overload:
- In this study, a low-carb, high-fat diet with nearly 40% of fat calories from saturated fat caused more significant improvement in liver fat deposits than a low-fat, calorie-restricted diet.
- This study in rats found that saturated fat did not cause fat accumulation in the liver, even when the rats ate a calorie surplus and gained weight.
If you get your saturated fat in the form of junk food, it probably comes with a hefty dose of sugar, and sugar does contribute to fatty liver. But the saturated fat is not to blame.
There’s not a huge amount of evidence for monounsaturated fat, but it seems to be beneficial. In this study, for example, subjects got either a high-carb diet (52% carbs, 18% protein, 30% fat) or a moderate-carb high-MUFA diet (40% carbs, 18% protein, 42% fat, and 28% MUFA). The high-MUFA subjects reduced liver fat noticeably more than the high-carb subjects.
As Paleo veterans can probably guess, Omega-6 fats are bad news. On the most basic level, they’re inflammatory, and inflammation is one of the many drivers of insulin resistance and the metabolic syndrome in general. This paper also goes into some of the other evidence linking Omega-6 PUFA to liver trouble in particular: the short version is that they’re really not great for you, and it’s best to minimize the amount of Omega-6 PUFA in your diet by avoiding seed oils, choosing grass-fed or pastured meat rather than factory-farmed versions, and treating nuts as an occasional indulgence rather than an everyday staple.
With Omega-3s, we finally have a clear effect: they’re beneficial. For one thing, they help improve the oxidation (burning for energy) of fat, so it doesn’t get stored in the liver. They’re also anti-inflammatory, and help counteract the damage of Omega-6s. The evidence in human trials supports this: in this study, for example, 1 year of supplementing with Omega-3 fats significantly improved the health of the patients’ livers.
To make a long story short, the evidence we have suggests that the right kind of fat isn’t dangerous at all to the liver. People with fatty liver disease often get told to eat a low-fat diet, but may actually be counterproductive, because on a low-fat diet, you’re almost guaranteed to be deficient in one crucial micronutrient strongly protective against fatty liver disease: choline.
Diet and Liver Disease: Choline
One of the major problems with many mouse studies of fatty liver disease is that they don’t account for micronutrients that also play a huge role in preventing (or causing) liver problems. All the micronutrients are important, but one of them is head and shoulders above the rest.
Choline is a water-soluble B-vitamin found abundantly in liver, other meat, and egg yolks. There’s also some in broccoli, cauliflower, and other cruciferous vegetables, but you’d have to eat a whole lot of broccoli to get the choline you need. Nutritionists originally thought that choline was an “optional” nutrient (since we have a metabolic pathway for making it), but considering the evidence that we have from patients on feeding tubes, we now know that isn’t the case.
This study dramatically demonstrates the role of choline in maintaining good liver health. Patients on feeding tubes are notorious for getting fatty liver disease. The researchers took four patients who had low blood levels of choline, and gave them a choline supplement for 6 weeks. Sure enough, their fatty liver disappeared completely with adequate dietary choline.
The amount of choline that an individual person needs depends partly on genetics and partly on sex. Some premenopausal women need less, because they have a gene that interacts with estrogen to make their body’s production of choline more efficient. But almost 40% of women don’t have this gene, and they need the same higher level of choline as men and postmenopausal women do: about 550 mg per day.
To put that requirement into perspective, it’s equivalent to roughly 6 ounces of raw beef liver or 5 egg yolks. If you wanted to get that choline from broccoli instead, you’d need to eat 3 pounds of broccoli, so animal foods are definitely a preferable source. This suggests that fatty animal foods don’t cause fatty liver disease; they help prevent it thanks to their high levels of choline! If you’re eating Paleo, you shouldn’t have a problem with getting enough choline – just enjoy the whole egg and don’t skimp on the organ meats. Ironically enough, eating foie gras could help your own liver get healthy!
Diet and Liver Disease: Gut Flora
This is a very new area of research, but there’s a growing body of evidence connecting NAFLD to imbalances in the gut flora.
This shouldn’t be surprising to the Paleo crowd: since gut flora are so heavily involved in the development of obesity, diabetes, and other metabolic disorders, it only stands to reason that they’d be important for NAFLD as well.
For one thing, the gut flora regulate the metabolism of choline, so how much choline you get depends on how happy your intestinal bacteria are. Gut barrier permeability (leaky gut) may also play a role: after an evaluation of several patients, this study concluded that NAFLD is associated with leaky gut, and also with the prevalence of small intestinal bacterial overgrowth (SIBO). This one concurred: patients with fatty liver had much higher rates of SIBO than controls.
There are several other mechanisms that could really use some more research (this paper goes into more details if you’re curious), but the take-home is clear: unhappy gut flora make for a very unhappy liver as well.
Summing it Up
The good news about fatty liver: if you can catch it as NAFLD (before it gets to NASH), it’s reversible. And the evidence we have suggests that Paleo nutrition covers a lot of important bases: it’s high in Omega-3s, low in Omega-6s, rich in choline (and other vital nutrients) and easy adjustable to meet anyone’s carbohydrate requirements. Probiotic supplements, bone broth, or fermented foods are also options to look into in terms of healing the gut flora.
A note on one common pitfall: if you do have fatty liver disease, you might notice a transient spike in cholesterol as your liver begins to heal. This is normal and nothing to worry about: it’s simply your body’s way of eliminating the cholesterol that used to be stuck around the liver. Your numbers will go back to normal once your liver is healed, and your arteries won’t be any the worse for it. It’s certainly no reason to panic and go back to a low-fat, choline-deficient diet!
Of course, none of this information is a substitute for medical advice. Diet is only one part of health; it's not a substitute for professional medical care. If you have fatty liver, you should talk to your doctor about diet and potentially medication: don't self-diagnose online and then start trying to treat yourself all alone! But hopefully this article will give you some information and references to bring with you into the doctor's office, so you can rest assured that Paleo is not making the problem worse!