Last night my foster son picked my brain regarding diabetes (his birth father is a Type 2 diabetic). While the entire car-ride conversation was ripe fodder for a blog post, what I’m going to recount here is our discussion on fatty liver, fructose, and diabetes.
What is fatty liver?
Fatty liver is an excess buildup of fat cells in your liver. When the liver becomes too fatty , inflammation occurs and liver function is compromised.
What does fatty liver have to do with diabetes?
They both are diseases of sugar metabolism. In Type 2 diabetes, your cells are insulin-resistant – they no longer respond to insulin’s attempts to pull sugar out of your bloodstream. In development of fatty liver, chronic high intake of fructose causes fatty deposits to develop in the liver.
Fructose is a type of sugar found in fruit (and in high fructose corn syrup, but we’ll get to this later). Chemically, it’s a simple sugar just like glucose but is metabolized differently. Glucose (and other sugars) are metabolized like this (courtesy University of Miami):
Fructose, however, follows a much shorter route:
Ok, I’m dramatically oversimplifying the fructose pathway , but I want you to understand the “big picture” concept here. What happens with excess consumption of all carbohydrates is that they get repackaged as fat through a process called de novo lipogenesis . However, there’s a limit to how much and how quickly sugar gets repackaged as fat – a rate-limiting step.
An analogy: Imagine a FedEx shipping plant with a huge fleet of trucks and piles and piles of boxes to be shipped. How quickly can you ship the packages? The number of workers packing the trucks would be your rate-limiting step. The boxes can only be delivered as quickly as the trucks are filled. It doesn’t matter how large a fleet you have to deliver boxes with, without workers to pack them, the packages can only drip-drip-drip out of the plant.
The rate of sugar metabolism (see above complicated diagram) is bottlenecked by the regulatory enzyme phosphofructokinase . Consume a ton of glucose, and what will eventually happen is that insulin rates rise, causing levels of leptin to rise, which limits your appetite. No appetite = you stop flooding the system with sugar (but not before the damage is done ).
Not so with fructose. Fructose, that lucky dog, gets to skip that step. Instead of having to be shuttled via the insulin pathway, fructose directly enters the liver and gets metabolized without this rate-limiting step. So if you consume a lot of excess fructose, your liver synthesizes a lot of triglyceride (fat). In fact, there’s practically no limit since insulin isn’t involved and thus your appetite won’t be blunted (recent research indicates that fructose effectively “shuts off” your appetite regulation ). So what happens? Fatty deposits begin to show up in the liver (undelivered “packages” sitting around in the plant warehouse) – and over time, inflammation and liver cell damage occurs. Continue this over time, and you’ve got the fertile breeding grounds for obesity and diabetes .
So does that mean if I eat fruit I’ll get diabetes?
It’s unlikely. Remember, we’re talking about excess consumption of fructose. Eat a bunch of fresh fruit, and you’re likely to consume 15-20 grams of fructose, tops. But with industrialization of food and the addition of high fructose corn syrup as the primary sweetener used in food manufacturing, daily intake of fructose is nearly 4 times higher. Think about all the possible sources of fructose – it’s in just about every sweetened drink you can think of: soda; fruit juices, iced tea, etc. Moreover, sucrose (table sugar) is 50% fructose. All that adds up to a considerable intake.
What it boils down to is that it’s easy to develop fatty liver (and diabetes) if you’re indiscriminate about what you eat and drink. Avoid sweetened drinks high in high fructose corn syrup, stay away from sugar, and you’ll likely be fine.
Let’s offer a Cliffs Notes version of the above:
This great diagram from the American Liver Foundation (via msnbc.com) says it all:
As a general rule, sugar is bad for you. But fructose is particularly bad. So disregard what the food companies tell you and stay away.