Cranky ol' judge presiding over Fat v. Sugar. (Photo: Shutterstock)

Before you throw the book at all sugars, let's refresh our memories on a few facts.

If you were around in the '80s and '90s you likely recall the low-fat diet craze. (Who didn't kill an entire box of SnackWell's pulling an all-nighter in law school?) Nutritional experts, government agencies and industry experts pointed the finger at fat as the culprit for our obesity epidemic and a slew of other health issues like diabetes and heart disease.

Today, we now know that fat is not the demon we once made it out to be, and, in fact, fat is a necessary part of our diet that helps control hunger, absorbs vital nutrients and helps fight against disease. Here's my previous post on making the case for fat.

Having acquitted fat, it's now sugar (most notably "processed" or "added" sugar) that sits in the witness stand and is taking the rap for our health problems. So let's review some hard facts about this fundamental molecule and our complicated, and sometimes emotional, relationship with it.

As always, before making any changes to your diet, please consult your doctor, nutritionist or dietitian.

What is sugar? And what about carbs? Sugars are molecules made up of carbon, hydrogen and oxygen atoms. They occur in nature and are vital for life, energy storage, brain function and all sorts of useful processes in both plants and humans. There are many kinds of sugars including glucose, fructose, sucrose (table sugar), lactose, etc. Sugars are a type of carbohydrate, but not all carbohydrates are sugars. Some carbohydrates in the body break down quickly into sugars and others more slowly. So not all carbohydrates behave the same way in our bodies.

Why are some kinds of sugars a problem? Sugars taste sweet to us, and that's why we love them. Most experts accept that we evolved to crave sugar and learned to gobble it up back when food was scarce. Naturally occurring sweet foods like fruit are loaded with good stuff like vitamins, nutrients and fiber. So it was a good survival hack to eat them whenever we found them.

But today's processed foods are packed with refined and added sugars. Why? Because they're tasty and make us eat more and buy more. And that can very easily push us into a calorie surplus and cause weight gain and health problems. Add to that the fact that we are the most sedentary, immobile, stressed-out generation in human history, and we've got a real problem.

Are all sugars bad? OK, here's where it gets complicated. Research now suggests that "processed" and "refined" foods high in sugar (like cookies, sodas, juice and basically anything found in your firm's vending machine) may act differently in the body than less-processed and unrefined foods, like fruit. What we're learning is that how sugars are packaged can impact how our bodies react to them. Studies are increasingly showing that, when sugar is eaten with good stuff like fiber (such as in fruit), it's absorbed slower and doesn't trigger a spike in fat storage like when we drink sugary sodas or eat brownies that lack dietary fiber.

Today's processed sugar, like high-fructose corn syrup, is not a health food to be sure; it lacks any real nutritional value and can easily stimulate overeating. But natural sugar, like that found in fruit, doesn't act the same way. Which is why it's easy to eat 10 cookies. But when was the last time you ate 10 apples?

The $64,000 question: Will sugar make me fat? Analyses and systematic reviews of studies show that, when protein intake and total calories are controlled, diets higher in carbs and sugars don't significantly contribute to weight gain. Meaning if we measure and control our total caloric intake, eating a higher carb and sugar diet doesn't make us fat. BUT, most of us aren't measuring our caloric intake. So when we free-range eat a diet high in carbs and sugars we tend to overeat and go into a big caloric surplus, which causes fat storage and health problems. If you aren't going to measure your calories it would be wise to behaviorally limit your sugar and carb intake. But remember, apples and brownies are different. A wise nutritionist once said to me, "No one ever got fat or sick eating apples."

How much sugar is OK to eat? This is hard to say. The best rule of thumb right now would be from the American Heart Association, which says men should consume no more than 9 teaspoons (36 grams or 150 calories) of added sugar per day and women should consume no more than 6 teaspoons (25 grams or 100 calories) per day. For context, one typical can of soda has 8 teaspoons (32 grams) of added sugar—about your entire day's allotment right there.

Keep in mind, however, that these were the same folks who decades ago said fat was the devil. Things are always changing with new research and studies. Also, it's important to note that reporting has shown the AHA and other agencies are heavily influenced by the powerful sugar lobby.

What about sugar substitutes? It would seem logical that low- or no-calorie sugar substitutes (like aspartame, sucralose or stevia) would be a better choice. But like all things it's not that simple. Experts are studying both artificial and natural sugar substitutes and finding some complex results including increased cravings, addiction, overeating, cancer and diabetes. For now, the safest, smartest choice for many of us is the rule of moderation and to try to limit our intake of these products in favor of "real" foods.

Jonathan Jordan is a personal trainer, nutrition coach and corporate wellness consultant in San Francisco. Check out his blog JJ Fit 24/7.