Junk food: What role does it play in a healthy diet?

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Chronic diseases such as cardiovascular disease, type 2 diabetes and certain cancers are responsible for almost 70% of all deaths worldwide. It makes sense that we’d want to better understand the risk factors that contribute to these diseases, especially when it comes to things that are within our control, including what we choose to eat.

We all intuitively know that unhealthy diets contribute to many of these diseases, but what does the science actually say?

Well, Chen and his colleagues took a look at all the studies done on ultra-processed foods to determine exactly how they affect our health.

What exactly are “ultra-processed foods”? These are foods that have been altered from their original state by multiple processes that could include rolling, puffing, grinding and pearling. Artificial colors, flavors, sweeteners and emulsifiers are often added. These give foods a longer shelf-life and also make them super attractive to our palates.

Examples include soft drinks, sweets and candy bars, chips, bacon, sugar-sweetened breakfast cereals and fries.

The bottom line from this study is exactly what you’d think – that the people who consumed the most highly-processed foods experienced the worst health outcomes.

And who were the people eating “the most”? Well, these were people who were getting 30% or more of their daily calories from highly-processed foods. So one-third of their diet was made up of junk foods.

Specifically, these people were much more likely to be diagnosed with heart disease, high blood pressure, strokes, metabolic syndrome, cancer (primarily prostate and colon cancers), depression and irritable bowel syndrome.

And they also tended die at a much younger age than people who consumed less junk food.

Chen and his colleagues looked at which countries were eating diets higher in ultra-processed foods. It may not surprise you to learn that it’s highest here in North America, with 57.6% of daily calories of the average American comes from junk food.

The rest of the world is not doing that much better:

  • France 35.9%
  • Mexico 29.8%

Finally, Chen and his colleagues explored why diets loaded with ultra-processed foods raise the risk of almost everything that can go wrong with our health.

They described two main reasons:

The first reason is that highly-processed foods are high in calories and they are designed to be easy to overeat. They are often loaded with unhealthy fats, sugar and salt. And they also tend to be low in fiber, vitamins, minerals, and other things that are good for us.

Food companies also literally engineer these foods to be hyper-palatable, meaning they taste so good to us, have exactly the right texture, and leave us wanting more. These foods also trigger our natural reward systems more than whole foods do. And that release of dopamine in the brain leaves us wanting more and more. It’s such a vicious cycle for us.

The second reason the researchers give is that ultra-processed foods can crowd out the more nutritious foods. If a big chunk of your diet is coming from soda and fast food, there’s less space for the nutritious stuff – the veggies, fruits, lean meats and other minimally-processed whole foods.

So the question that remains is “is there room for junk food in a healthy diet?”

And my answer to this is that the dose makes the poison. If you are eating a healthy, balanced diet with adequate healthy fats and protein, getting your veggies in, and you’re progressing towards your goals, then having a processed treat every now and again isn’t going to do you much harm, and in fact, in may even help keep you on track.

But if the rest of your diet is composed of chicken nuggets, milkshakes and Doritos, then you’ll definitely see improvements in your health and your weight if you replace some of that ultra-processed stuff with real, whole foods.

I want to also emphasize, though, that saying “never” to junk food often backfires on us. For many of us, blacklisting foods just makes us want them even more. So instead of looking at these foods as a no-go, look at them as foods you want to eat less of. And what “less” means will be different for each one of us, depending on what our current diet is.

But a general rule of thumb to follow is to try to keep ultra-processed foods to 10-20% of your diet, with minimally-processed whole foods making up the rest.

If you’re like the average North American and are nowhere near that yet, though, you can’t really expect yourself to just all of a sudden flip a switch and just be there. Instead, you want to focus on being just a little bit better. We’re looking for progress, not perfection here.

So look for ways you make small changes to your diet. Small ways you can replace ultra-processed foods with less-processed foods. This could be things like:

  • Adding extra veggies to your pizza or ordering thin crust
  • Eating a piece of fruit before you open the bag of chips
  • Have carbonated water with a splash of juice instead of drinking a can of soda
  • Try a rotisserie chicken instead of a bucket of fried chicken

Making these small substitutions make not feel like massive action to you, but when you start doing these little things consistently, over time, they add up and you see big changes.

And finally, I just want to end this by offering you one last thought. Oftentimes, a diet loaded with highly-processed foods can really be a symptom of a deeper problem. And so before you commit to making any changes to your diet, it can be helpful to just take a step back and ask yourself why you’re eating those foods in the first place.

Is it because you’re too busy to prepare food at home? Or are you perhaps snacking to soothe feelings of loneliness, anger, sadness, or some other emotion? Or are you trying to burn the candle at both ends and eating to stay awake? Are you finding yourself eating all the homemade goodies colleagues bring to work? Or maybe you live somewhere where it’s difficult to get wholesome foods.

In any case, by taking a close look at why you eat the foods you do, you’ll be better able to plan the strategies that will work best for you and your unique circumstances.


 Chen X, Zhang Z, Yang H, Qiu P, Wang H, et al. Consumption of ultra-processed foods and health outcomes: a systematic review of epidemiological studiesNutr J2020; 19(1):86.