In many ways, looking into matters of health and fitness and writing this column is like being a PI. After all, the end result of either job is the same: to provide you, the client, with important knowledge.

But since you don't pick my assignments or pay me to pursue them, it might be more accurate to call me a public, rather than a private, investigator.Much of what I've learned about doing investigative work has come from Spenser, the super sleuth in a series of novels written by Robert B. Parker. In these, Spenser often discusses cases in terms of what, through his experience, instincts, and evidence, he knows is true and what, in a court of law, he can prove is true.Quite often, he discovers the first far sooner than the latter, yet he can not notify the police until he has both.That's where this job is different. If I wait for proof the way it's defined in the court of health-and-fitness law, after handfuls of both short- and long-term studies that overwhelmingly support the notion, not only is the element of timeliness lost, but something else may also be as well.Your health.Case in point is the back-and-forth battle about high-fructose corn syrup (HFCS). Superimpose a chart of the increase in overweight Americans since the early 1970s over America's increase in consumption of HFCS since that time, and they look strikingly similar.My gut as well as working with dozens of people who wanted to lose weight tells me that's more than coincidence, and dozens of studies since the 1970s seem to support that, such as one published in December 2011 issue of Metabolism.In that study researchers compared the effects of a 24-ounce beverage sweetened with HFCS to one sweetened with what you know as table sugar. The HFCS beverage produced higher amounts of what researchers call "metabolic biomarkers," a situation that increases the odds of a whole host of health problems, such as high blood pressure, kidney disease, and diabetes.Yet less than three months later, a review of more than 40 studies published in the Annals of Internal Medicine article seemingly cleared HFCS of its critics' primarily concern: that it leads to the weight gain that often triggers the aforementioned illnesses. That's because in 31 of the 40 studies, the subjects given HFCS ate the same number of calories as the control subjects and gained no more weight.In short, I can't prove those studies wrong even though they contradict something I "know" in my gut. All I can do in this case is create cogent, commonsense arguments to sway you away from using nothing more than minimal amounts of HFCS and focus the majority of my columns on things more clear cut.Like the link between a lack of sleep and weight gain.Back in 2003, a University of Michigan study caused a stir when researchers discovered that every additional hour third graders spent sleeping reduced their risk of becoming obese sixth graders by 40 percent, a finding that supported earlier work at the University of Chicago. In that study, sleep-deprived adults produced more of the hormone ghrelin, which produces hunger, and less of the hormone leptin, which signals satiety.More recently, researchers have established that losing as little as 60 minutes of sleep a night for three days produces the hormone problem that the University of Chicago study uncovered.A study funded by the National Institutes of Health, Minnesota Obesity Center, and the Mayo Clinic and previously mentioned in a May "Fitness Master" column found subjects who slept 80 minutes less for eight nights ate an average of 549 extra calories each day than normal. Compounding matters and contrary to what you would expect being awake the extra time did not increase their daily caloric burn significantly.In fact, a Swedish study that disrupted adults' sleep found the disruption caused the body to hoard calories and lower basal metabolic rate to such an extent that subjects burned 20 percent fewer calories the next day.Consider all these studies and you see that not only does a lack of sleep reduce the body's need for calories, but it also leads to you consuming more of them.Perhaps the most intriguing study linking a lack of sleep to weight gain was performed by researchers at the University of Washington Medicine Sleep Center using information reported by 1088 twins, 604 identical and 484 fraternal. The researchers considered less than 7 hours of sleep a night to be "short" sleep, 7 to 8.9 hours to be normal, and 9 or more to be "long" and looked for patterns.Beyond finding that those who slept more weighed less, the findings suggested that a lack of sleep makes you more likely to be influenced by your genetics. In other words, dieters from families whose family members tend to be overweight are more susceptible than typical to a lack of sleep undermining their weight-loss efforts.