We know food matters to our health — but how do we find sound advice on what to eat?

They say, “an apple a day keeps the doctor away.” As with most sayings it doesn’t tell the full story but does reveal a kernel of truth: what we eat is important to our health. Most of us would acknowledge as much, but it is still difficult to know exactly what we should and should not eat. We hear about the latest trend diets and see food advertising all around us. What should we believe when it comes to food advice?

The answer is simpler than you might expect and probably sounds a lot like what your parents told you as child: eating more plants like fruits and vegetables and less packaged and processed foods promotes good health.

Understanding why this is the case takes a bit more explanation and knowing might help us shift to and stick with a healthier diet. Plants have more of the things important to good health like vitamins, minerals and fiber. Whole foods that haven’t undergone extensive processing have fewer of the additives that can be harmful in large quantities like sugar, salt and saturated fats.

Plants are 'superfood'

In the late 1800’s and early 1900’s scientists linked many diseases with dietary deficiencies. For instance, scurvy, a disease that often affected sailors on long ocean voyages, was determined to be caused by a lack of vitamin C in the diet. After the discovery, many ships began carrying citrus fruit and distributing lemon or lime wedges to their sailors to prevent scurvy. British sailors even took on the nickname “limeys.” Over the years many more vitamins have been discovered and most can be found in the plants we eat. More plant-based, whole food means more nutrients and antioxidants for your body.

Processed foods can lose some of their 'goodness'

Highly processed foods can lose some of what makes them healthy. Consider the difference between eating an apple and drinking apple juice. A whole apple contains fiber which slows the release of sugar as it is digested. The fiber also benefits the digestive system, reducing things like diverticulosis, hemorrhoids and even colon cancer risk. On the other hand, juice has been processed, eliminating the fiber, so we miss out on the benefits. The lack of fiber also leads to large amounts of sugar being released to the body all at once, challenging the body to prevent spikes in blood sugar.

Additives can detract from health

In the mid-1900’s the medical community began to link dietary over-consumption with the development or worsening of some medical conditions. Diets high in simple sugar often contributed to diabetes. Diets high in salt increased blood pressure. Diets high in saturated fats were linked to higher rates of cardiovascular disease like heart attacks and strokes. Nutritionists began recommending that patients with diabetes eat fewer carbohydrates and simple sugars; that patients with cardiovascular disease eat less fatty food to lower cholesterol; and patients with high blood pressure consume less salt.

But as processed foods have come to make up a greater portion of the American diet, restricting these additives is challenging. Consider the difference between eating a potato and tomato versus eating French fries dipped in ketchup. The French fries have been fried in oil and sprinkled with salt. Adding ketchup means even more salt as well as added sugar with each bite. The added sugar can impact blood sugar; the added salt can raise blood pressure; and the added oil and saturated fat can raise cholesterol and risk for cardiovascular disease. A little of this food may not have a big impact but eating it regularly or in high quantities can be a drag on good health.

Protein source matters

Eating a diet rich in protein can be a way to reduce carbohydrate intake, maintain lean muscle and manage weight, but some protein sources are healthier than others. The World Health Organization has recognized red meat (coming from a mammal) and processed meat (like hot dogs, sausage, salted meat or smoked meat) for their increased risk of causing cancer. The American Heart Association recommends limiting the consumption of red and processed meats because they have been linked to cardiovascular disease. They recommend alternatives like fish or nuts or if you do eat meat, a lean meat like chicken.

Plants can be a healthy source of protein that also help reduce meat consumption. One reason is they have less saturated fat. Consider the difference between eating almonds and green peas versus eating a steak. The steak has lots of saturated fats – it can usually be seen on the cut of meat and in the pan after cooking. The effect of consuming this saturated fat is to raise cholesterol levels, a risk for cardiovascular disease. Breakdown of saturated fats also leads to other substances that increase inflammation, which has been linked to increased rates of cardiovascular disease as well as pain levels and risk for some cancers.

What does the evidence tell us?

One of the first serious attempts to study a specific diet came in the 1970’s with Dr. Ornish who studied over 20 years how a strict diet and lifestyle program could improve cardiovascular outcomes. In recent decades many diets have been studied, and studied more rigorously, including the DASH diet (Dietary Approaches to Stop Hypertension) and the Mediterranean diet. The specific details of the diets have varied, but the evidence shows some consistent results: healthy diets include more plants and less processed food. Healthy diets are associated with improvements in blood sugar, cholesterol, blood pressure, cardiovascular events, weight management and even risk for some cancers.

Making a change for the long-term

Most diets will lead to some amount of weight loss because they restrict which foods a person can eat, usually leading to a calorie reduction. Unfortunately, many people will regain the weight once they abandon the diet. Researchers have begun to study the health consequences of frequent weight fluctuations. A healthy diet should be sustainable for the long-term and should do more than just help with weight management.

It is difficult to change diet overnight, and even after a change, can be difficult to sustain. The good news is that most people don’t need a radical change in diet. Even small changes that are maintained over time can have big impacts. I emphasize three things with my patients about diet: which foods they choose to eat, how much they eat at a time and how frequently they eat it. It is unrealistic to expect someone will completely give up their favorite food, but if that food isn’t the healthiest option, it is reasonable to have that food less often and/or reduce the portion size when eating it.

There is more than one way to eat healthy. Many of my patients have come up with creative solutions to improve their diet. Some skip animal protein one day per week, “Meatless Mondays,” or avoid animal proteins before dinner. Others fill up on salad before moving onto other courses. At my house we keep a bowl on the counter stocked with fruits, vegetables and healthy nuts for a quick snack.

I like to frame the issue of a healthy diet as adding more of the good things which naturally leaves less room for the things we want to cut back. Hopefully it gives new meaning to the advice we often give children: eat a generous serving of vegetables before moving onto dessert.

Peter Barkett, MD, practices internal medicine at Kaiser Permanente Silverdale and writes a regular column for the Kitsap Sun. He lives in Bremerton.

This article originally appeared on Kitsap Sun: A doctor's advice when it comes to nutrition, diets and good health