We’ve published in other posts the role exercise and glut-4 transporters play in opening muscle cell channels to glucose in an insulin independent manner. This is important, as via this physiology the body can simultaneously oxidize fat and carbohydrate at dramatically higher levels, for improved endurance.

Over the past 30 or more years multi-billion dollar companies have been formed under the ‘sports nutrition’ banner. Industry players built their businesses on the back of simple sugar formulations, product positioning for everyday use, and pervasive consumer access. Business exploded, as sugar-laden beverages marketed under sports nutrition got consumed anytime in the day, increasingly outside of physical activity periods. So why the problem?

The Glut-4 transporters are a very important part of human physiology, as they’re critical to moving glucose out of the circulatory system (where it’s highly inflammatory) and into the muscle cells for oxidation. There are two ways this happens,

  • At rest, when food or drink with carbohydrate is comsumed, insulin is secreted, and triggers these glut-4 transporters to move to the cell edge, and open the channels to allow glucose to move from the circulation into the muscle,
  • The other mechanism, is, after exercising for 30-60minutes, muscle contractions and muscle contraction by-products also trigger glut-4 transporters to move to the cell edge and open these same channels, but notably WITHOUT insulin. This is why exercise is so good for treating insulin resistance, and type2 diabetes. This is also the foundation, of simultaneous oxidation of endogenous (in muscle cells or liver) carbohydrate and fat (muscle, or fat cells), since there is little-no insulin secreted to stop fat oxidation.

However, there are some compounds in, or added to foods and drinks, that at rest or during exercise, suppresses the effectiveness of glut-4 transporters – they are, fructose and maltodextrin.

Here’s some foods with typically higher fructose and/or maltodextrin levels:

  • sports/energy drinks,
  • nutrition bars,
  • fruit juices,
  • pop/soft drinks,
  • fruits like pears, mango, cherries,
  • dried/canned fruits (also in muesli),
  • sweetened yoghurts,
  • honey,
  • sauces (like ketchup, grill marinades etc.),
  • salad dressings,
  • and, obviously candies (check your granola bars) are full of it, specially high fructose corn syrup blends.

In animal studies, exercise training has shown to improve glut-4 by over 50%. Adding fructose to that training, suppresses that exercise improvement, by 20-30%. Similarly for maltodextrin. In human studies, a diet with higher fructose consumption for only 4 weeks, caused a 27% decrease in glut-4.

To connect all the dots here, the reason why this issue is worth pointing out, is how many sports-nutrition products are full of fructose and or maltodextrin. A number of sports drinks mix fructose and maltodextrin in trying to deal with the known gut issues of consuming these sugars in higher amounts during racing, and high intensity training. The reason manufacturers are pushing athletes, to take high amounts of these carbohydrates, is because every time you train on these carbs, you’re suppressing both your fat oxidation efficiency and your glut-4 transporter improvement.

This is why at SFuels, our science based approach to training, is to train on low/no carbohydrate (SFuels Train) to stimulate efficient fat oxidation, and for high intensity training and racing, conduct that first 30-60mins without carb, opening up the glut-4 transporters, so that you can optimally burn fat and carbohydrate (SFuels Race+) for the remainder of the training session or race. Here’s our QuickStart guide to read up on the science, practical guidance on how to do this, and some reference case studies.

Replace Fructose with a better alternative.

So what to do in a practical way to replace high fructose foods and ingredients with better alternatives? Here’s a set of great recipes that give you plenty of sweet morning, lunch and dinner options, check them out here in our latest LIFE Guide.

Be well. Go Longer. Team SFuels.