How to see if you are a carb or a fat person:

  • By Brian Keane

Finding the right fuel source for your muscle is a must. Your fuel can affect not only how your muscle utilize energy, but also whether your muscle builds up or breaks down. The analogy I like to use is what happens when you put petrol into a diesel car? The car slowly breaks down and stops working. Fuelling your body is the same thing.

Not fuelling your body properly can lead to a sluggish metabolism (which can massively impair fat loss) and can hugely reduce strength and overall energy. Your muscle can use all food groups (carbs, fats and proteins) as fuel, but it has its priorities; for example, some people will work better of a higher carbohydrate / lower fat diet, others will work much better on high fat / low carb diet. It really varies person to person and it’s worth experimenting yourself.


It’s actually relatively simple to test out. I would set aside three or four days to experiment with the example below:

Try including a moderate to high dosage of quality complex carbohydrate (sweet potato, oats, brown rice etc.) alongside a quality protein source (lean meats or fish for example) in every meal and see how you feel. Ask yourself, what are your energy levels like? Do you feel bloated or sluggish or do you feel amazing with this type of eating and have more energy than you know what to do with?

If the latter is the case, then it’s highly likely that you run better of a high carbohydrate diet. For example, Paul, The Head Trainer at Brian Keane Fitness is a high carbohydrate person, as soon as he drops his carbs below 100g, his energy levels drop, his brain doesn’t function as well and he just doesn’t feel as good. However, when he goes anywhere between 300g and 500g every day, he feels and looks amazing.

I on the other hand can lower my carbs to nearly zero and still feel amazing; eating 300g- 500g of carbs every day makes me feel horrible, bloated and full.

But on the flip side, but as soon as my fats decrease, my energy drops; my brain function becomes impaired and I just don’t feel as good.

Paul and I have nearly the exact same lifestyle, we both focus and love high intensity training, we don’t eat processed food and prioritise health above all else; yet we are on completely opposite ends of the spectrum when it comes to fats and carbohydrates.


Photo of me and Paul after we did 8 hour of burpees to raise money for charity in April this year. 

Experiment with three or four days of high carbs (50-100g per meal depending on your weight) and see how you feel. If you feel like I do (bloated, full and tired), it’s more likely that your body runs better of fat as its primary (or secondary if you include protein) fuel source.

That being said, this is a massive generalisation- for example, digestion, insulin sensitivity, overall training program and systems will all have a major factor – for example when I competed and won my fitness model pro card at the Miami Pro Universe Championships in 2014, I would train twice a day for four hours a day. This made me incredibly insulin sensitive and my body sucked up carbohydrates like a drink through a straw during this time. This is a good experiment to run to give you a gauge on what your body prefers; I always felt that knowing if your body runs better of carbs or fats is like having the answers for a test you’re taking, you’re obviously going to get a much better result when you know the answers for the questions coming up.


As useful as it is to understand if your body runs better of carbs or fats, its critical to understand that what you put into your body becomes your fuel source.

If you feed your body with quality, nutrient dense food that’s free from artificial additives, sweeteners and preservatives- then your body is going to work at its optimal level. On the contrary, if your body is using processed and low quality foods as its energy source, then it’s going to work at a low quality level.

“The food you eat can be either the safest and most powerful form of medicine or the slowest form of poison” – Ann Wigmore


Building lean muscle or losing body fat is relatively simple (simple, not easy) – simple in the since that if you give your body quality, nutrient dense foods and exercise at a higher intensity your body composition will change.

You body is always going to prioritise ‘allowing you to stay alive’ as opposed to ‘allowing you to look amazing’ – your body hasn’t evolved to understand or process these additives and preservatives that are now added to most commercial foods- we’ve been on this planet for thousands of years- those preservatives and additives have been around for 50, maybe 60 years – some of us have grandparents older than that!

When you eat foods that your body doesn’t recognise, it has to use all of its energy to break it down safely (this is why people that eat a lot of processed food have no energy) and 99 out of 100 times shuttles straight it directly to fat pockets (where is furthest away from vital organs, thereby keeping your safe or ‘alive’). We store most of our toxins in our fat stores – that’s why visceral fat, explained in the ‘Eliminating Reasons For Fat To Exist’ section of the book is dangerous to your health.

Now that you understand what’s happening internally, think about it from a logical standpoint. Your body’s primary job is to keep you alive but you want to be leaner, lose body fat, and build muscle or what your physical goal is. Breaking down highly processed foods and ingredients is literally given your body one extra job to do but what happens when you remove this job from the equation? Suddenly your body isn’t focused on worrying about breaking down these ingredients that it thinks could potential kill you. What happens then?

Look at it this way.

What if I asked you to ‘sweep the kitchen floor, hang out the clothes and cook the dinner and I want to you do it all in twenty minutes’, what would happen? Well, you would end up doing one of the jobs, maybe starting into the second but would probably completely neglect the third OR worse, you would do all three jobs really poorly.

Now, what if I asked you to just sweep the kitchen floor and you have the same twenty minutes to do it, what would happen? That floor would be probably be spotless because you wouldn’t be worried about or focused on the other jobs. Your body is the same. Replace the three jobs with ‘breaking down processed food, losing body fat and building muscle’ and the same outcome holds true. Take away one job (breaking down processed foods and ingredients) and suddenly your body becomes very efficient at either burning body fat or building muscle (or pretty good at doing both) as there’s one less job to do.




You are always your own best example and I can say that this is probably my biggest factor (alongside resetting your metabolic set point, talked about in an earlier chapter) in being able to sustain and maintain a low level of body fat with a good level of functional, quality muscle year round. My body only has to really worry giving me enough energy through the day, if I eat fewer calories, I lose more body fat, if I eat more calories, and I build more muscle. I cut all processed foods and ingredients a good time ago and have luckily reaped the benefits since; now I have more energy, my mind is clearer and my body is performing better than it ever has. Try cutting all processed food for six weeks and see how your body and mind responds; by all means, you are more than welcome to go back on it after six weeks but I have a feeling you probably wont.

Brian Keane Fitness Podcast

Brian is a qualified personal trainer, sports nutritionist and strength and conditioning coach.

He is the best selling author of the book The Fitness Mindset and currently travels the world as a professional speaker. He also hosts the #1 podcast The Brian Keane Podcast.

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