Some false health-and-fitness notions just refuse to die. One, in fact, has managed to live on for more than 40 years after an illustrious adherent said adios to this world specifically because of it.

Large amounts of endurance-based exercise do not - I repeat, do not - allow you to eat anything you want in any amount.If you don't believe me, ask Jim Fixx, the long-distance runner who became famous by anticipating the onset of the running craze and writing The Complete Book of Running. Oops! There's a bit of a problem with that.Fix, who ran up to 80 miles a week after being an overweight smoker until his mid-30s, infamously died of a heart attack way back in 1984 because he believed logging mega miles allowed him to eat anything he wanted - including staggering amounts of sugar - despite a family history fraught with heart disease.So he ate foolishly for years and then went out for a run one day and never returned. He was discovered at the side of a road, dead from a massive heart attack.Now you'd think all types of endurance athletes would've learned from Fixx's flawed logic, but based on my experience that's far from the case. Consider the behavior of a group of guys from Berks County who meet for weekend bicycle rides that I join on occasion.The ride leader often creates a 50-to-60-mile ride that has a coffee stop someplace past the midway point. If that's the case, I say my goodbyes and pedal on.The others enter and have more than coffee. They "carb up" by chowing down on a pancake-sized cookie or two. Or a bear claw bigger than twice the size of a real bear's claw. At one stop known for its sticky buns, two guys save a bit of money by ordering a whole pan and wolfing down three each.These guys know how I feel about nutrition, so they will poke fun at their pig-outs.With false pride, one rider once told me that he consumed only black coffee on one stop. Before I could respond, he laughed and admitted that he had only done that to save room for the milkshake and soft pretzel he had on the car drive home after the ride.While I reminded you of Fixx's infamous demise to grab your attention, the type of health troubles you're more likely to encounter if you do as Fixx did probably won't be as dramatic. More likely, you'll encounter them later in life as I'm afraid my buddies from Berks will.How soon that occurs could simply be a matter of your present body weight.A number of the aforementioned Berks County riders - despite spending six or eight or 10 hours a week in the saddle and expending as many as 5,000 calories a week through exercise - are five, 10, or even 15 pounds overweight.And those mega shots of sugar-laden calories two-thirds of the way through their long ride are partially the cause.Even though these guys think they're getting energy to finish the ride from their sugar blasts, that energy is temporary at best. As this column has explained a number of times, consuming simple carbs in abundance causes such a dramatic rise in blood sugar that your body responds by secreting so much insulin that not just some but nearly all of the sugar gets taken from the blood stream to be used as energy.The end result, as Levi writes, in an article published in the April issue of Health titled "This Is You on Sugar," is that your "energy surges and then bottoms out."So do you know what my Berks County buddies often do once they get back from a ride? They consume more sugar-laden foods not only because they are feeling a lack of energy, but also because "eating sugar [in excess during the ride] leads to the release of dopamine, the neurotransmitter that makes us want more of it."A pattern like this makes them and you a prime candidate for a disease you definitely want to avoid: type 2 diabetes. But the typical American diet seems to steer you toward rather than away from it.Consider that recent research done at UCLA found that 16 percent of middle-aged Californians already have the disease. Even more troubling may be that 60 percent of the middle-aged Californians who don't have its precursor called prediabetes.Furthermore, the UCLA researchers estimate that seven out of every 10 people with prediabetes progress to full-blown type 2 diabetes - despite the fact that type 2 diabetes is the type that can be thwarted with the proper lifestyle changes.Such as not eating foolishly just because you burn a ton of calories during exercise.