Eat plenty of fruits and vegetables. That’s about the only health mantra that remains constant. Sugar is blacklisted, but eggs are back. Our bodies need fat but the right fat. It seems that nutrition experts are always changing the rules. Here are some of the hottest health trends and some science behind them.

Sugar

Loading up on added sugar - sweetener that doesn’t occur naturally in food - is a major don’t. It appears on nutrition labels as high fructose corn syrup, cane sugar, agave nectar, honey and too many others to list here.

“The health advantage of naturally occurring sugar is the company it keeps with lots of fiber and a host of healthy vitamins and nutrients,” said Dr. Stephen Devries, a preventive cardiologist and executive director of Gaples Institute for Integrative Cardiology in Deerfield, Ill. “Fiber found in fruits and vegetables cuts the amount of sugar that is absorbed.”

As the experts point out, we need glucose to fuel everyday living, but not sucrose, which is the fructose and glucose found in added sugars. The body metabolizes all added sugars the same way, causing insulin - the hormone that says “store fat!” - to shoot up without the stabilizing effects of the fiber, protein and nutrients provided in natural foods.

The American Heart Association suggests that women get no more than 24 grams of added sugar daily. Men should aim for less than 36 grams. To put that in perspective, one 12-ounce can of Coke has 39 grams of sugar, which is more than 150 percent of a woman’s daily recommended amount.

Currently, there is no differentiation between natural sugar and added sugars on a Nutrition Facts Label, but the Food and Drug Administration is proposing a requirement to list the amounts of added sugars and to also force companies to declare a daily percentage value.

Fruit vs. fruit juice

When you eat a medium banana, you’re ingesting about 14 grams of sugar in the form of fructose. That sugar is wrapped in fibrous material that slows down digestion. On the other hand, an 8-ounce glass of apple juice contains no fiber and up to 39 grams of sugar. The liver is the only organ that can process fructose, so too much can overload your system and result in insulin-resistant, or Type 2, diabetes.

Fruit juice in small amounts most likely won’t be a problem for a healthy, lean individual, but juices have just as many calories and sugar - and sometimes more - as sweetened sodas. Stick to getting your juice from the whole fruit instead.

Artificial sweetener

The jury is still out on what effect artificial sweeteners like saccharin (Sweet’N Low), sucralose (Splenda) and aspartame (Equal) have on the body, but research suggests it is not innocuous.

“The gut bacteria fueled by artificial sweeteners send chemical signals to the liver to make more sugar,” Devries said. “As a result, although artificial sweeteners themselves don’t contain sugar, they can trick the body into making more.”

Recent findings by the Weizmann Institute of Science in Israel suggest artificial sweeteners might alter the bacteria in our gut, disrupting the body’s ability to regulate blood sugar.

“Another concern with artificial sweeteners, specifically sorbitol and xylitol, commonly found in sugar-free gum and candy, is that they can worsen IBS symptoms, including diarrhea, gas and abdominal bloating,” said Jessica Schultz, a registered dietitian at University of Chicago Medicine.

She suggested stevia as a sweetening option. “Stevia, a small green leaf that is naturally sweet and virtually zero calories, can be grown all year round. We are currently growing this ultra-sweet plant in our work garden. I like to muddle it with mint and add it into my iced tea.”

Fat

Our bodies need fat, but where we get it is important. Omega-6 fats, the kind found in processed foods, should be limited. Most vegetable oils, including soybean, corn and safflower, are high in these fats and should be avoided. “A diet high in omega-6 fats will likely be lower in omega-3 fats,” Schultz said. “(Omega-6 fats) may increase inflammation and the incidence of disease. Ideally you should aim for an anti-inflammatory diet with a higher ratio of omega-3 to omega-6. A few examples of omega-3-rich foods include flax seed, chia seed, walnuts and wild-caught fatty fish.”

Increasing intake of omega-3 fats encourages fat burning and reduces the amount of insulin in the blood.

Processed vs. unprocessed

Almost all food is processed in some way, but what this term refers to is chemically processed food. Think of a banana versus a 100-calorie banana bread snack pack. It also refers to the chips, cookies and breads that can stay seemingly forever on grocery shelves.

“Many processed foods are devoid of fiber, so the added sugar they contain causes blood sugar levels to soar,” Devries explained.

Schultz added that “they tend to be high in calories, sodium and unhealthy fats that can lead to inflammation.”

Eggs

A summary of the 2014 meeting for the Dietary Guidelines for Americans says, “Cholesterol is not considered a nutrient of concern for overconsumption.” What does this mean? Mainly that the cholesterol in your food is not a main influence on the cholesterol levels in your body, so don’t worry about eating those egg yolks for breakfast.

Red meat

An offending culprit in red meat - steak, lamb, hamburgers - is L-carnitine, according to a study by half a dozen U.S. medical centers and published in Nature Medicine. When the body ingests red meat, it provides certain gut bacteria with the resources to make trimethylamine-N-oxide (TMAO). Researchers found that TMAO could accelerate atherosclerosis, or the buildup of plaque in your arteries.

The corn and soy diet most cows are fed also leads to an increase in omega-6 content in the meat, Schultz explained.

“When buying meat, I generally recommend (joining) a meat CSA (Community Supported Agriculture),” she said. “A meat CSA allows consumers to buy grass-fed, sometimes organic, local protein at a reasonable price while supporting good quality farming practice.”