Why You Can’t Burn Off a Bad Diet

Why You Can’t Burn Off a Bad Diet

There are two main factors to consider when seeking to lose weight or maintain a healthy weight: diet and exercise. We live in a fast-paced world and one where we like to get instant gratification for our efforts, but our health, and especially our weight, doesn’t often give us the instant results we want. 

Add to that all the unhealthy packaged foods lining the shelves of stores all over the country, and it’s easy to see why so many people struggle with their weight. 

I am often asked by patients what is the best way to lose weight, and so often, they’re looking for that magic answer that will allow them to continue eating bad foods, get in their daily exercise, and see results. But while exercise is extremely important to our health, it’s only really 20% of the weight-loss equation. Let’s take a look at why: 


Let’s do the math

We all know that calories in minus calories burned = weight loss, weight gain, or maintenance – but so often people fail to do the math, so let’s do it together. 

The average burger and fries contain 900 calories. Add in the soda for a whopping 1050 calories for the entire meal. If that was your only meal of the day, you’d be under-eating, but let’s be realistic and say that it’s one of three meals. Unless you’re incredibly active, or have high muscle mass, your daily recommended intake of calories will sit somewhere between 1500-2200 calories. Suddenly, that fast food meal is at least half your daily calories. 

So how long does it take to burn 1000 calories?

  • Walking uses around 250 calories an hour (assuming a walking speed of around 3 mph) so that’s 4 hours to burn 1000 calories.
  • Running at 5mph ramps up the burn rate but you are still talking 2 hours, and 2 hours is a long time to run! 
  • Serious strength training falls in between, so 3 hours would burn 1000 calories. Three hours in the gym every time you eat a burger? Who has the time?

So how about the healthy option? Say you ate a 6oz salmon fillet with a cup of broccoli for a total of 300 calories. Now the math looks better: 

  • Walking for just an hour will burn 300 calories.
  • Running at 5 mph will burn off the meal in 30 minutes.
  • Strength training uses 300 calories in 45 minutes – pretty much the average time for a gym session.


Fast food is not your friend

Yes, it’s convenient, yes, it tastes good, but it just isn’t good for you. We all love it, but that’s because most of it is stuffed full of sugar and salt. It contains high amounts of these two because they provide instant gratification to our taste buds and give our systems a shot of energy.

Fast food is also deficient in many of the micronutrients that our bodies and brains need to function at their optimum levels. If a high percentage of your diet is fast food, and the same is true of many TV dinners and other quick-to-make convenience foods, you’re getting a lot of calories and not a lot else.

In terms of weight control, it has far too many carbs and fats to be anything other than an occasional – that’s very occasional! – naughty treat.


Why a healthy diet helps weight control

Eating healthy food is the polar opposite of majoring on fast food. Not only will you enjoy the health benefits of an abundance of those essential vitamins and minerals but you will reduce your carb intake massively. The major problem of fast food is that its salt and sugar are hidden. When you eat a burger and fries you are not thinking sugar and you are not thinking salt but they are both there in quantity. You could make the same meal from scratch at home, and it would, generally, have far fewer calories. 

There are no hidden calories in fresh healthy food. Of course, some of them contain natural sugars but not in the enormous amounts that you find in a burger and fries accompanied by a soda. The calories are fewer and more controllable and fewer calories means you are less likely to put on weight.

Did you know that a 12oz soda contains 25% more sugar than the recommended amount an adult should have in a day? That’s just one 12oz soda!

Healthy food doesn’t mean tasteless and boring food though it may mean you need to retrain your taste buds, or at least become a little more familiar with your kitchen. Most people who cut out sugar soon find that things they once found tasteless are suddenly sweet. 

There is also the problem of addiction. Studies have shown that sugar is addictive, the more the body consumes, the more it craves. This can cause problems for anyone seeking to reduce their sugar intake but most can “kick the habit” in just a few days. 

The bottom line is while both diet and exercise can work together to aid weight loss it is what you eat that wins the big changes for you. When you opt for healthy foods, you can actually eat more and stay fuller for longer. It’s a win-win. 


Dr. Nancy Rahnama, MD, ABOM, ABIM, is a medical doctor board certified by both the American Board of Obesity Medicine and the American Board of Internal Medicine. Her specialty is Clinical Nutrition, that is, the use of nutrition by a medical doctor to diagnose and treat disease. Dr. Rahnama has helped thousands of people achieve their goals of weight loss, gut health, improved mood and sleep, and managing chronic disease. 

Curb & Burn