Diet or Exercise: Which is Most Important for Fat Loss?

Tom MacCormick
Written By: Tom MacCormick
February 20th, 2020
Updated: May 28th, 2021
Categories: Articles Fat Loss
13.5K Reads
Diet or Exercise: Which is Most Important for Fat Loss?
If you had to choose one way to achieve fat loss would it be through your diet or through your exercise? Let's discuss which is more important.

It’s a new year and most gym rats are thinking about building a summer body. After the over-indulgence of the festive season many of us could do with shedding a few pounds of unwanted fat. Fat loss is the name of the game for most people at this time of year. The good news…Fat loss is simple. The bad news…it isn’t easy.

When all is said and done the most important factor for successful fat loss is consistently creating a calorie deficit. A caloric deficit is when you consume fewer calories than are required to maintain your current body weight.

A calorie deficit can be achieved by:

  1. Reducing intake
  2. Increasing expenditure
  3. A combination of both points 1 & 2

If you consistently achieve a calorie deficit then you will lose fat. Pretty simple, right?!

So, what is the best way to achieve a calorie deficit? Diet or exercise?

Some experts like to give out percentages or ratios to describe the contribution of diet and exercise. For example, it is frequently said that fat loss is 80% diet and 20% exercise. Meanwhile, Dr. Shawn Talbott states that, “As a rule of thumb, weight loss is generally 75 percent diet and 25 percent exercise”.

Spoiler alert: If you want to optimize your results, you’ll pay attention to both. In that respect, I fall firmly into the camp of saying fat loss is 100% diet AND 100% exercise.

When you eat and train right there is a synergistic effect. Your fat loss efforts result in a 1=1=3 effect. In other words, you look even more awesome when you combine smart nutrition plans with effective training protocols. This is because you not only lose fat, but also preserve muscle mass. To my mind, that is the real goal of a sensible fat loss phase for physique conscious trainees.

But what if you had to choose just one? Which gives you more bang for your buck?


The Case for Diet: Crunch the Numbers

It is much easier to cut calories than to burn them off. Eating smarter to create a 500-calorie deficit requires some degree of restraint, but is achievable for everyone. Burning 500 calories through exercise however, requires a significant investment in time and effort.

For example, it equates to more than four miles of running for the average guy. Given that a pound of fat contains about 3,500 calories that means you’d need to lace up your sneakers and run over four miles a day to lose a pound a week if you kept eating at maintenance. When all is said and done you’re looking at running over a marathon a week for one lousy pound!

Research shows that exercise alone is ineffective for the average person. You can, however, get lean simply by restricting what you eat, but the risk is that you will end up skinny. Nobody wants that!

Related: How To Build A Fat Loss Meal Plan: A Step-by-Step Guide

I can vouch for this from personal experience. As a 22-year old semi-professional rugby player I suffered a serious knee injury. I was unable to train and on crutches for 12 weeks. During this time, I followed a very restrictive diet. I basically only ate when somebody else offered to make me some food.

The hassle of trying to hop around the kitchen, on one foot without falling over meant making meals wasn’t a risk I was prepared to take. I usually made myself a bowl of cereal in the morning and then, got a sandwich off a visitor, and relied on my parents for dinner. I was probably only eating 1,200-1,600 calories most days.

Before the injury I was eating north of 4,500 calories to maintain my weight at about 215lbs. During the recovery from injury I got shredded, but I also lost a ton of muscle mass and ended up weighing only 180lbs!

Fat Loss Workouts

The Case for Exercise

Just because you can get lean without exercising doesn’t mean you should. While the calorie burn of exercise isn’t as high as many people think, it can still play a role in fat loss. It just isn’t very effective to focus solely on the calories burnt side of the energy balance equation. After all, you cannot out-exercise a bad diet. With that said, it is still worth noting that hard training does contribute towards energy expenditure and can help create a calorie deficit.

Exercise is an important component in maximizing fat loss while minimizing muscle loss. Without it, there is a high chance that a large chunk of your weight loss is coming from muscle and bone density.

Related: What Happens to Fat When You Lose Weight?

Since training stimulates growth of those metabolic tissues, it creates a powerful signal to retain muscle mass and preserve bone density. Losing weight through exercise means you’re burning mostly fat and keeping your gains. Lifting weights is the most effective way to preserve muscle mass when in a calorie deficit.

To build a big and lean physique you need to combine a sensible diet with smart training. When both are combined they create a synergistic effect where fat loss is accelerated and muscle mass is retained. The key thing to understand here is that strength training helps you to retain muscle mass. This is its key role during a fat loss phase. It is not a particularly effective way to burn lots of calories.

Since we’ve established that diet and training should be combined for optimal results, you’re probably thinking, ‘what type of exercise should you do to maximize fat loss?’

Fat Loss Workouts Are Dumb!

It is tempting to focus on burning as many calories possible when working out in a fat loss phase. This has led to people creating “fat loss” workouts. In all honesty, I think this is dumb! The calorie burn of a single workout is relatively minor when compared to showcasing some dietary restraint. One candy bar equates to about 30 mins of high-intensity training. It is much more efficient to skip the candy bar than it is to try and burn it off.

Instead of doing silly fat loss circuits or hours of cardio, I suggest you utilize the gym to send a muscle building (or at least retaining) signal. Lift weights and make it your goal to try and build muscle while dropping body fat. Unless you’re a beginner you won’t actually build significant muscle mass while in a calorie deficit, but you will retain it. Doing so means you look big and lean at the end of your fat loss efforts instead on skinny.

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This means the training prescription during a fat loss phase is to take a “what built it best, retains it best” approach. Thus, your training shouldn’t look dramatically different in a bulk to a cut. Think of training as the car and diet as the steering wheel. You’re always training in a manner to attempt to build muscle, but your diet dictates if you gain or lose weight.

To hammer this point home, cardio style training is pretty poor at muscle retention. In one study, splitting groups into a diet + cardio group and a diet + resistance training group, both groups lost weight, but the cardio group lost 9 lbs of lean mass! Meanwhile the resistance training group actually gained 2 lbs of lean mass.

Another study split participants into one of three groups.

  1. Diet only
  2. Diet + cardio
  3. Diet + resistance training

All of these groups lost weight, but only the diet + resistance training group preserved their lean mass. Furthermore, a 2015 meta-analysis found that diet + resistance training has a greater effect on improving body composition than diet alone or cardio and diet.

In light of this data, my recommendation is that diet changes rather than training changes should be used to create the calorie deficit and strength training should be used to preserve muscle mass. This has a few benefits:

  • It’s easier to measure and more efficient to control energy balance through diet
  • Resistance training should be done to gain strength and muscle mass, not used to simply increase energy expenditure
  • Increasing training volume significantly to burn extra calories interferes with recovery capacity. When in a calorie deficit this could result in negative effects on hormones that increase the risk of muscle loss &/or impede fat loss
  • Cardio can be an effective tool to create a calorie deficit but, is not effective at retaining muscle mass so, shouldn’t be the primary mode of training for developing a muscular and lean physique

The bottom line: Diet and exercise work synergistically to optimize fat loss. Want to end up with a muscular, strong, and shredded physique? Focus on both diet and exercise, but if time is limited remember that what matters most is what you eat. It’s much more efficient to reduce your calories through diet than it is to try and burn them off through exercise.

Trying to “out-exercise” a bad diet is never a smart move! All the training in the world will not help you lose fat if you are stuffing donuts in your face faster than Homer Simpson.

  1. Bryner RW, Ullrich IH, Sauers J, Donley D, Hornsby G, Kolar M, Yeater R. Effects of resistance vs. aerobic training combined with an 800 calorie liquid diet on lean body mass and resting metabolic rate. J Am Coll Nutr. 1999 Apr;18(2):115-21.
  2. Hunter GR, Byrne N, Sirkikul B, Fernandez JR, Zuckerman PA, Darnell BE, Gower BA. Resistance training conserves fat-free mass and resting energy expenditure following weight loss. Obesity (Silver Spring). 2008 May;16(5):1045-51
  3. Clark JE. Diet, exercise or diet with exercise: comparing the effectiveness of treatment options for weight-loss and changes in fitness for adults (18-65 years old) who are overfat, or obese; systematic review and meta-analysis. J Diabetes Metab Disord. 2015 Apr 17;14:31.
1 Comment
Aanand suman
Posted on: Mon, 02/24/2020 - 08:01

Thanks sir, you give us a lot of important knowledge that we are missing.