Back in 2010, Professor Mark Haub, of Kansas State University, lost 27 pounds (12.2kg) in 10 weeks eating a diet made up up primarily of junk food. He ate 1,800 calories per day, made up of Twinkies, Doritos, sugary cereals and Oreos. Not only did he lose a lot of weight, he also improved some of his key health markers, including cholesterol, triglycerides and body fat percentage.
So what does this tell us about fat loss?
Calories matter. A lot.
As it pertains to fat loss, calories are undoubtedly the most important consideration. Whilst it is advised to select your foods from far healthier sources, you can absolutely lose body fat on a diet comprised primarily of junk food, provided you ear eating in a calorie deficit.
The second interesting point to note is that very often health will improve with weight loss. As you can see with the example from this study, his cholesterol improved despite eating primarily junk food that was high in fat and sugar for 10 weeks.
We need to stop thinking in absolutes as it pertains to nutrition for fat loss. There are no 'good' or 'bad' foods per se. There are no foods that will 'stop' you losing fat. What matters is what you do most of the time.
If you ever find yourself eating what you might consider food that is 'bad' for you, you can stop thinking that it is going to ruin your diet and sabotage all of your fat loss efforts.
So whilst I am not advocating this type of approach to dieting, hopefully it illustrates two key concepts: -
1. You need to ensure you are eating the correct amount of calories in order to lose weight & this should be your prime consideration above all else, and;
2. Your diet can be comprised of a vast array of foods that can include some processed, 'junk' food, provided you adhere to point #1. It might be easier to stick to a fat loss diet knowing you don't have to base your diet solely around white meat and broccoli.
Here are a few reasons why eating a diet of mostly un-processed, whole foods, with a high protein intake will be advantageous...
1. Satiety: Junk food is often extremely high in calories, but very low in nutrients. They will do very little to quell hunger. However, a higher protein intake will help stave off hunger, making the overall dieting experience easier.
2. Muscle Mass Retention: A higher protein intake will help you retain your muscle mass, which is crucial to the fat loss process.
3. Health: Whilst Mark Haub's health markers did improve throughout the duration of the 10 weeks, I would suggest that if he had continued with this diet over a longer time-frame he would have seen diminishing health. Eating a nutrient dense diet is going to support training performance, provide more energy and boost your immune system.
TLDR: To lose body fat, pay attention to calories above all else. For longer-term health and well-being ensure you eat mostly whole, un-processed foods in the knowledge that some 'junk' food isn't going to kill you.