Sugar is poison. Right?
If you watch the latest food documentary on Netflix or read the headlines in the news, you will be convinced that sugar, especially fructose, is the root of all nutritional evil. As with most things in life, the reality is a little more nuanced.
First it’s important to understand some context about sugar and how it affects the human body. On food labels you will find more than 20 different types of added sugars, but at a fundamental level there are three types of sugar: glucose, fructose, and galactose.
Glucose is the most basic form of sugar in human metabolism. Your body converts the carbohydrates in food to glucose, which can be used for energy in the body or stored for later. If your doctor measures your blood sugar levels, she is looking at the amount of glucose in your blood, which is normally just less than one teaspoon. Galactose is a form of sugar commonly found in dairy products, paired with glucose to form lactose. It is also found in smaller amounts in fruits, vegetables, and beans.
Fructose is present naturally in fruit and honey. Fructose is better known for its presence in soft drinks and other calorie-containing beverages in the form of high-fructose corn syrup. Fructose is often cited as problematic due to its unique fate following absorption from your digestive tract. Fructose is absorbed in the small intestine but shuttled off to your liver for processing before it hits your bloodstream. Contrast this to glucose, which is dumped directly into your bloodstream ready for your body to use as energy.
Why does it matter that fructose goes to your liver first? Because your liver must metabolize it. During this process one of the byproducts that is created is uric acid, which is known for its role in causing gout. Excess uric acid can also increase blood pressure. Some research has shown associations between the number of sugar-sweetened beverages a person drinks and increases in blood pressure.
As the fructose is processed, your liver will try to store the resulting glycogen, but your liver is only so big and it can store only so much sugar. Excess fructose is turned into fat and shipped off into your bloodstream in the form of triglycerides. Elevated triglycerides is a major risk factor for cardiovascular disease and a component of metabolic syndrome, the union of symptoms that combines heart disease and diabetes and is plaguing our population. From a metabolic standpoint fructose seems toxic as it directly increases compounds that drive increases in blood pressure and heart disease.
Fructose is also considered dangerous because it does not does flip the same satiety switches in your body that glucose does. Advocates of the danger of fructose often point to animal studies that show having fructose before a meal will drive you to eat more calories. It would seem that fructose is poison and consuming lots of fructose will cause you to gain weight.
The Reality of Fructose
There are two major issues with the doom and gloom associated with fructose. They are dose and context. Much of the scientific data showing the dangers of fructose are not relevant to you and the amount of sugar or fructose that you eat or could even dream about eating on a daily basis. For instance, in order to experience a rise in triglycerides from eating too much fructose, research shows you would have to drink almost five cans of soda each day. But even if you aren’t drinking that much soda, what about the negative effects of fructose on blood pressure? An analysis of the 15 available controlled clinical trials did not find any unique effect of fructose versus any other carbohydrates on blood pressure.
When looking at the effects of eating a particular nutrient, like fructose, it is always important to remember that we eat foods. These foods contain a variety of different nutrients that will be eaten together. Fructose is rarely eaten in high levels all by itself. Even the highest fructose-containing soft drink at your local drugstore, Dr. Pepper, is 60.2% fructose. Only in a lab would you eat or drink high amounts of pure fructose. The real world danger of consuming too much fructose would happen in conjunction with consuming higher amounts of glucose. At this point you just have a problem with eating or drinking too much sugar from any source, not specifically fructose.
Along those lines, if you look at how our nutritional habits have changed since the 1970s, when high-fructose corn syrup hit the market, you would see that there have been numerous shifts in our dietary habits, but the most striking is how many more calories we are consuming. American adults are eating upward of 600 calories more per day! One key piece of information that we often forget about the body is that overeating changes “the game” of our metabolism. If you overeat by 600 calories per day, it doesn’t much matter if it’s from kale or cola as you are still in a calorie excess. When you eat as many calories as your body needs, there is much more nutritional forgiveness. A review of 31 clinical trials found that if you are eating the amount of calories that your body needs (and not in excess of that), then eating more or less fructose has no real consequence for your body weight. This points to the fact that weight gain isn’t specifically caused by eating more fructose; it’s caused by just eating more. The problem that presents itself to us is that that it is very easy to overconsume, which we cheerfully do, beverages with high amounts of fructose and glucose (e.g. colas, sweetened teas, energy drinks, sports drinks, etc).
A review of 31 clinical trials found that if you are eating the amount of calories that your body needs (and not in excess of that), then eating more or less fructose has no real consequence for your body weight.
Fructose also doesn’t automatically make you eat more either. One study gave participants a fructose or glucose drink and then gave them access to a room with a buffet. Over the course of two and a quarter hours, the people who drank the glucose drink ate 500 calories more than the people given the fructose drink! A more recent review of scientific studies looking at fructose and its impact (or lack of impact) on fullness found that there are so many different variables at play in our food life that it is currently impossible to create a compelling case for fructose being less satisfying than glucose.
What About You the Individual?
One of the problems with nutrition research is that it speaks in generalities. Often the larger the study the less relevant it can be to you the individual. What I have found through the research that I have helped conduct and the clients that I have worked with is that the only study population that really matters in the end is the study population of one—you. This doesn’t mean that research isn’t valid (I’m definitely not saying that), but it does mean that you need to filter information through the context of your life, digestion, metabolism, experiences, and genetics.
One recent study published in the journal Molecular Metabolism looked at peoples’ response to fructose and levels of a compound called fibroblast growth factor 21 (FGF21), and the results reinforce the individualized nature of diet and health. FGF21 is currently the center of cardiometabolic research, as elevated levels in humans has been associated with metabolic disease, suggesting that increased FGF21 is indicative of an “underlying metabolic stress.” In the study, researchers had 21 people drink high levels of fructose, glucose, or a combination of the two, as you would get in most sugar-sweetened beverages. Fructose caused the largest increase in FGF21 levels. In addition, participants in the study who had metabolic syndrome had higher default levels of FGF21, leading to further exacerbations due to fructose consumption. This suggests that people may vary in their sensitivity to sugar and its effects on the body.
This type of fructose-tolerance test is not readily available for people, but what can you do in the interim? Focus on your total sugar intake. Americans eat five times more glucose than fructose. If you are overconsuming fructose, then chances are you are overconsuming a lot more glucose. Be mindful of your calories. Don’t drink them. The primary source of fructose in the American diet is from calorie-containing sweeteners. I’m not just talking about high-fructose corn syrup. This also includes table sugar, honey, grape juice, apple juice, and pear juice. These are not quality calories that nourish your body. Each of these (except apple and pear) is made up of at least 40% glucose, too. Far second and third place on the fructose consumption list comes fruits and vegetables. I’ve never had to tell a client to stop eating so much whole fruit because he is getting too much fructose. It isn’t going to happen. Enjoy whole fruits and vegetables. Don’t worry about the headlines. You know your body best, so nourish it to support your unique needs and goals.