In 2009 Robert H. Lustig, MD, UCSF Professor of Pediatrics in the Division of Endocrinology, presented a seminar for the UCSF Mini Medical School for the Public called Sugar: The Bitter Truth.
Below is my summary of what he presented. The seminar is one and a half hours long and you can watch it here Sugar: The Bitter Truth. In my opinion this is critical viewing, and I strongly urge you to take the time.
If you have concerns about the following information, do discuss them here, but remember this is Robert Lustig's research that I am summarising.
Since the 1970s, as fat has been reduced in our diet, sugar and carbohydrate consumption has increased. Fat used to provide the flavour, and sugar has taken its place.
We have reduced our fat intake, but rates of obesity metabolic syndrome (obesity, type II diabetes, lipid problems, hypertension, cardiovascular disease) have all gone up. Why?...
"It ain't the fat people, it ain't the fat." It's the carbohydrates. Sugar.
In the 1970s we learnt that dietary fat increased LDLs ("bad cholesterol"). An increase in LDLs led to Cardiovascular Disease. And so we were told to decrease our fat intake. HOWEVER:
We now know that there are actually 2 kinds of LDLs, the neutral ones, that have no effect on our arteries, and the "bad guys." Dietary fat increases the number of neutral LDLs. And guess what increases the bad guys? Carbohydrates. But, we decreased fat in our diets, and replaced it with carbohydrates, specifically - sugar. And that was the worst thing we could do.
Read that again and again until you get it - it's crucial!
So what is wrong with sugar?
Sugar is 50% glucose and 50% fructose. Glucose is good. Fructose is bad.
When you eat glucose, 80% of the calories are taken up and used by all the organs in the body. Every cell in the body uses glucose. It is the energy of life, and it is what we were supposed to eat.
20% goes to the liver. And the liver can handle any amount of glucose that is thrown at it. Maybe about half a calorie ultimately gets stored as fat.
When you eat fructose, 100% of the calories have to be metabolized by the liver. The rest of the body can't deal with it. When an entire compound has to go to the liver because only the liver can metabolize it, and in the process it creates a variety of problems, we have a name for this... we call it a poison.
30% of fructose calories end up as fat.
Chronic fructose consumption leads to:
type II diabetes
increase in uric acid causing gout
increase in blood pressure and therefore hypertension
fetal insulin resistance
habituation, if not addiction
The way fructose is metabolized and the problems it leads to are extremely similar to those of chronic ethanol exposure (heavy drinking).
Fructose does not suppress the hunger hormone. Your insulin doesn't go up, your leptin doesn't go up, and so the brain does not know that you have eaten and therefore you eat more. We are eating more and more and we don't know when to stop. Thanks to sugar.
As fat has been reduced in our diet and sugar increased, fibre has also been decreased. It's too slow to cook, too slow to eat, and decreases a product's shelf life. But fibre reduces the negative effects of fructose. We should be eating our carbohydrates with fibre. So don't worry, fruit is OK: "when God made the poison, he packaged it with the antidote" - fruit contains both fructose and fibre.
Fruit juice is stripped of fibre. So you can pour fructose down your throat, or down the sink. Dr Lustig's first recommendation for reducing and removing fructose from your diet is to pour your juice down the sink.
Fructose is a carbohydrate, but it is metabolized like a fat.
"A high sugar diet is a high fat diet"
A few further points:
You can't exercise enough to burn the calories you are eating. This is pretty much impossible. ("C'mon, 20 minutes of jogging for one chocolate chip cookie. You can't do it. Are you joking me?") Exercise is important because it reduces obesity for more complicated reasons (see video at 1hr 11 mins). But it doesn't burn calories.
If you are living and eating in the USA you have one massive High Fructose Corn Syrup problem. You should watch this whole video (specific details are at 17 mins and at 1hr 11 mins).
If you are interested in the LDL/cholesterol discussion:
for the reasons explained above regarding the 2 types of LDLs, Lustig suggests tryglicerides are a better measure of cholesterol than LDLs (low TGS and high HDLs are good, high TGS and low HDLs are bad). You may have picked up that this LDL discussion has massive consequences for our diet, regarding more than just sugar. That's a topic for another day.
And finally. In the North and South Magazine article "What's Making us Fat. Surprising new discoveries on why we gain weight" by Donna Chisolm (November 2012, great timing huh?!) we are told this:
The American Heart Association recommends a daily intake of 9 teaspoons of sugar a day for men, 6 for women, and 3 for children. We have a median intake of 30 for men, 24 for women, and 26 for children.
We should probably do something about that.