This is your body on fast food


A client recently asked me, “How often can I get away with eating junk food?” She knows that my “80:20 rule”: Eat healthy at least 80 percent of the time, but enjoy the occasional less healthy food no more than 20 percent of the time.

I’ve seen this approach work well with my clients who were previously chronic dieters yet hadn’t been able to lose weight. Once I give them permission to have “forbidden foods,” they’re able to make healthier choices the bulk of the time.

There is some evidence that “cheat meals” (I hate that term) can help boost fat loss and mental health among dieters. Yet I wanted to give my client a better answer. Could a few days of junk food or a single fast food meal make a difference in your health?

Junk food and fast food defined


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“Junk food” is food that is highly processed, high in calories and low in nutrients. It’s usually high in added sugars, salt and saturated or trans fats. Some evidence shows it’s as addictive as alcohol and drugs.

“Fast food” is food prepared quickly and eaten quickly or taken out. Although there are a growing number of healthier fast food options, most fast food can still be classified as junk food.

• Long-term effects of eating junk food: Eating a poor quality diet high in junk food is linked to a higher risk of obesity, depression, digestive issues, heart disease and stroke, type 2 diabetes, cancer, and early death. Frequency matters when it comes to its impact on your health.

A review of studies on fast food and heart health linked eating fast food more than once a week to higher risk of obesity, while eating fast food more than twice a week was associated with a higher risk of metabolic syndrome, type 2 diabetes and death from coronary heart disease.

This is disturbing considering nearly half of American adults eat fast food at least once a week.

It’s human nature to think about benefits and risks over the short term. So how does junk food affect your body in the short term?

• A few days of junk food: Just a few days of junk food can change your metabolism. A small study of 12 healthy young men found eating junk food for just five days led to a reduced ability of their muscles to turn glucose into energy, even though they didn’t eat more calories. Over the long term, this change could lead to insulin resistance and type 2 diabetes.

Another effect is poor digestion. Because junk food lacks fiber, eating too much of it can lead to constipation.

• One junk food meal: That single fast food meal can narrow your arteries, leading to an increase in blood pressure. And the quick spike in blood sugar from eating foods high in refined sugars causes a surge in insulin, leading to a quick blood sugar drop. That leaves you tired, cranky and hungry for more.

Just one serving of junk food can increase inflammation throughout your body. An Australian study suggests that in people with asthma, a fast food meal high in saturated fat can increase inflammation in the airway, potentially making an asthma attack more likely.

Every healthy meal helps

The amount of inflammation and oxidative stress your body experiences after eating occasional junk food is a function of the your long-term choices.

If you want junk food once in a while, look at your habits. Do you smoke or overdrink alcohol? Are you exercising regularly and eating plenty of vegetables, fruit, legumes, fish, nuts and seeds and whole grains? You can “get away with” occasional junk food more easily if you follow a healthy lifestyle most of the time. So think about your ratio of healthy foods. Are you achieving 80:20 or is there room for improvement?

Every meal is an opportunity to positively impact your health.

Based on current research, my advice remains the same: Once you’re aware of all of the short-term and long-term impacts of junk food, you still really want some, have it less than once a week and savor it. Then get back to enjoying nourishing foods.