When I was 17, I became a vegetarian. A lifelong animal lover, I could no longer bear the thought of killing animals to fill my plate. So I banished all animal products from my diet. Still, the foods that I ate were far from healthy. In college, I didn't know much about preparing vegetables or understanding nutritional needs, so my meals were primarily of the pre-packaged boxed-pasta variety.

I was a vegetarian, but my overall nutrition was probably worse than if I had continued to eat meat. Fortunately, I switched up my diet about the time I moved out of the college dorms and started experimenting in my own kitchen. I've often wondered what effect that first foray into vegetarianism had on my health.

A recent observational study took a look at various forms of vegan and plant-based diets and confirmed my fears: Not all plant-based diets are good for you. When you think of someone who is a vegan, you probably assume they eat nothing but salads, beans and nuts each day. But as my experience shows, you can still be a vegan and follow a "plant-based" diet without ever touching an actual plant.

To understand the difference these diets can have on health, researchers at the Harvard T.H. Chan School of Public Health gathered dietary questionnaires from 210,000 nurses and other health professionals every two years for over two decades. They categorized three different types of plants-based diets:

  • Overall plant-based: Emphasized the consumption of plant-based foods with a reduced intake of animal products
  • Healthful plant-based: Plant-based with a focus on eating healthy whole grains, fruits and vegetables
  • Unhealthful plant-based: Plant-based with a high-level of consumption of less-healthy plant-based foods, such as refined grains

Researchers found that following a plant-based diet helps to protect against heart disease. But not every form of plant-based diet will offer this protection. Participants who followed the overall plant-based diet had an 8 percent reduction in heart disease risk, while the risk was reduced by 25 percent for those who followed a healthful plant-based diet. For those who consumed an unhealthful plant-based diet, the risk of heart disease increased by around 32 percent.

By teasing out the differences in plant-based diets, researchers uncovered two key points. First, you don't have to follow a completely vegan diet in order to receive some benefits to your health. Swapping the meat out of meals even just a few times a week can help reduce your risk for heart disease.

Second, a plant-based diet that is high in refined grains is actually more harmful to your health than one loaded with meat. Even if you remove all of the meat from your diet, you're doing more harm to your health than good if you're not getting most of your nutrition from healthy plant-based foods.

So bring on those Meatless Mondays. Just make sure that you're swapping your meat out for fruits, veggies, legumes, beans and healthy whole grain foods.