Avoid fructose to lose fat for summer. Fructose is a sugar that is found in large quantities in processed foods in the form of high fructose corn syrup, but it is also present in fruit. The body responds to fructose, especially large quantities of it, by turning it straight into fat. It also alters liver function, and if you eat large quantities regularly, it will render the liver incapable of processing glucose, meaning you’ll get even fatter in the long run.
A number of new studies remind us why it’s so important to eliminate all high fructose corn syrup from the diet and limit fructose intake from fruits to very moderate amounts. A study in the Journal of Nutrition looked at how the body processes sugars by giving lean and healthy participants a breakfast drink that was either 100 percent glucose, half glucose and half fructose, or 25 percent glucose and 75 percent fructose.
In the four hours following ingestion of the drinks that contained fructose, lipogenesis, or the production of fat in the body, increased significantly more than following consumption of the glucose drink. Not only was all of the fructose that the participants consumed at breakfast turned into triglycerides to be stored as fat in just four hours, but the body processed the food that the participants ate at lunch differently as well.
After eating a normal lunch, triglycerides stayed elevated by as much as 30 percent, indicating that the body was in a “fat storing” mode. Basically, all of the carbs that were consumed at lunch were taken by the liver, broken down, and then turned into fat.
These results are especially significant because the participants were lean and healthy, but their metabolism was significantly altered by just one large fructose dose in the morning. People who eat processed foods that contain high fructose corn syrup will have persistently altered metabolism that is in “fat storing” mode, and once you are overweight, your body will always favor fat storage.
Even more disturbing, a second study in the American Journal of Physiology found that if you eat a high-fructose and high-fat diet, you will become insulin resistant, meaning your body won’t process glucose efficiently either. This study found that after eating a diet high in fructose and fat for eight weeks, the liver will become ineffective at turning it into glycogen to be stored for future use.
In a healthy liver, when you eat glucose, the liver will decide whether the body needs to burn the glucose immediately for energy, store the glucose as glycogen for later use (a good outcome because you can call on those liver glycogen stores when doing very intense training and energy stores are low), or turn it into fat. A high fructose diet that also contains a lot of fat makes the liver incapable of synthesizing glycogen and it will be stored as fat instead.
Don’t be fooled by anyone who tells you that eating small amounts of high fructose corn syrup is okay. You need to save your fructose intake for fruits since they provide so many antioxidants, essential vitamins, and fiber. Plus, no one can go wrong eliminating all processed foods that are the most common source of high fructose corn syrup.
Don’t eliminate fruit, but if you are trying to lose weight or are concerned about your metabolism, limit fructose from all sources to 5 to 10 grams a day. For very active individuals, 20 to 30 grams of fructose should be the maximum intake. Berries are your best bet for fruit because they are low in fructose and are jam-packed with antioxidants.
Coate, K., Scott, M., et al. Chronic Consumption of a High-Fat/High-Fructose Diet Renders the Liver Incapable of Net Hepatic Glucose Uptake. American Journal of Physiology. 2010. 299(6), E887-898.
Parks, E., Skokan, L., et al. Dietary Sugars Stimulate Fatty Acid Synthesis in Adults. Journal of Nutrition. 2008. 138(6), 1039-1046.