THE FAT LOSS MYTH BUSTER

Keto, Fasting, Low Carb and Everything In Between

By Gary O'Daly  |  Gaz Gaelic Guide

Right, Let's Sort This Out Once and For All

Every few months there's a new diet trend that the internet tells you is the key to dropping body fat fast. Keto. Intermittent fasting. Cutting all carbs. Eating only at certain times of the day. And every single one of them has someone online swearing blind that it's the only approach that works.

Here's the thing though. None of them are magic. And all of them can work. But only for one reason, and that's a calorie deficit.

I'm going to break down the most popular approaches out there, explain what they actually are, how they work, and what the research says. And then I'll tie it back to the one thing that makes or breaks any fat loss plan, which is your energy balance.

No nonsense. No hard sell. Just the information you need to make a smart decision that actually suits your life as a GAA player.

Calorie Deficit: What It Actually Means

Before we get into the different diets, you need to understand the basics. A calorie is a unit of energy. Your body burns a certain amount of calories every day just to stay alive, move around, train, and do your job. That number is your Total Daily Energy Expenditure, or TDEE.

If you eat more calories than you burn, you gain weight. If you eat fewer calories than you burn, you lose weight. That's it. That's the whole game.

The Mayo Clinic puts it plainly: if you eat fewer calories and burn more through physical activity, you lose weight, (Mayo Clinic, 2024) and a starting point of roughly 500 calories below maintenance is a common recommendation across most obesity guidelines.

Now, where people get confused is they think certain diets break this rule. They don't. What they do is make it easier or harder to stay in a deficit, depending on the person. That's an important distinction.

Research published in PMC looking at optimal diet strategies for weight loss confirmed that an energy deficit is the most important factor in weight loss, (Kim & Bae, 2021, PMC8017325) regardless of whether that deficit comes from cutting fat, cutting carbs, or any other approach.

For a GAA player, your TDEE is probably higher than the general population. If you're doing two or three training sessions a week plus a gym, plus your day-to-day job, you could easily be burning 2,800 to 3,500 calories a day. That matters when you're deciding how aggressive to be with a deficit. I always say to lads, don't go crazy with the cut in season. A 300 to 500 calorie deficit is plenty. You still want to be fuelled for training and for the game.

The Ketogenic Diet (Keto)

What is it?

The ketogenic diet is a very high fat, moderate protein, very low carbohydrate approach. We're talking typically under 50 grams of carbs per day, sometimes as low as 20. To put that in context, a single banana has around 25 to 30 grams of carbs. So this is extremely restrictive on the carb front.

When you restrict carbs this dramatically, your body runs out of its preferred fuel source, which is glucose from carbohydrates, and shifts into a metabolic state called ketosis. In ketosis, your liver converts stored body fat into ketone bodies, which then become your main energy source.

How does it work?

According to a 2022 review published in Signal Transduction and Targeted Therapy, researchers have proposed several mechanisms for keto's effect on fat loss, including reduced appetite from the higher satiety effect of protein, reduced fat storage due to improved insulin sensitivity, and increased fat burning due to elevated lipolytic enzyme activity. (Masood et al., 2022, Nature Signal Transduction)

Basically, your body gets better at burning fat as fuel. Insulin levels drop, which matters because insulin is a storage hormone. Lower insulin means your body is more likely to tap into fat stores.

The initial weight loss on keto tends to be fast, and that gets people excited. But a big chunk of that early drop is water weight. Carbohydrates are stored as glycogen in your muscles and liver, and glycogen holds water. Cut the carbs, deplete the glycogen, lose the water. It can be a few kilos in the first week or two alone.

A meta-analysis comparing keto and low-fat diets over 12 months found that the keto group lost only 0.91 kg more than the low-fat group (Malinowska, Journal of Nutrition and Metabolism, 2024) over the long term, which is a fair bit less dramatic than the internet would have you believe.

Does it work for fat loss?

Yes, but not because it breaks any laws of physics. It works because most people find it easier to eat fewer calories when they're eating high fat and high protein foods that are more satiating. You eat a big plate of eggs, salmon, and avocado and you're not starving an hour later the way you might be after a bowl of cereal.

The research is consistent: when calories are matched, keto doesn't have a meaningful advantage over other diets. When calories are not matched, it can help people naturally eat less.

Should a GAA player go keto?

In my opinion, probably not in season, and definitely not without careful thought. Carbohydrates are your primary fuel for high-intensity sport. GAA is an intermittent sprint sport. You need glycogen in your muscles to repeat those sprints, make those runs, and stay sharp in the last quarter.

I'd be very wary of any GAA player going full keto during a competitive season. You might drop some weight initially but your performance on the pitch could suffer. There's a reason elite teams aren't putting their players on keto diets.

Intermittent Fasting

What is it?

Intermittent fasting, or IF, isn't really a diet in the traditional sense. It's more of an eating pattern. Rather than focusing on what you eat, it focuses on when you eat. You cycle between periods of eating and periods of fasting.

The most popular version is 16:8, meaning you fast for 16 hours and eat within an 8-hour window. So if your last meal is at 8pm, you don't eat again until midday the next day. Other versions include 5:2, where you eat normally five days a week and significantly restrict calories on two non-consecutive days.

How does it work?

The main reason IF helps people lose fat is simple: it shrinks the window in which you can eat, so most people end up eating less overall. That's a calorie deficit by the back door.

A 2022 meta-analysis in Frontiers in Nutrition compared IF to no dietary intervention and found that IF produced meaningful reductions in body weight, (Gu et al., Frontiers in Nutrition, 2022, PMC9108547) but crucially, when calories were matched between IF and standard daily calorie restriction, the differences in weight loss were very small.

A 2025 review also noted that simply shifting eating hours without creating a calorie deficit does not guarantee effective long-term fat loss, (Brasse et al., Cureus, 2025, PMC12740946) which again points back to energy balance being the deciding factor.

There are some potential secondary benefits beyond just the calorie reduction. Some research points to improved insulin sensitivity and metabolic markers with IF, and there's ongoing interest in the role of autophagy, a kind of cellular cleanup process that fasting may trigger. But for most people using IF for body composition, the main driver is just eating less.

Does it work?

For a lot of people, yeah. Particularly people who aren't big breakfast eaters anyway. If you're someone who trains in the evening, skips breakfast naturally, and eats your first meal around lunch, you might already be doing a loose version of this without realising it.

The issue is that some people compensate. They fast until noon and then eat massive portions for the rest of the day and end up in the same calorie ballpark as before. That's not a calorie deficit, that's just rearranged eating.

Should a GAA player use IF?

It depends on your training schedule and how your body responds. If you're training in the morning, training fasted is not ideal. You'd want some fuel in you before a session, particularly if it's a gym session with power work or sprints. Training in the evening? There's more flexibility.

The 16:8 approach can work well in the off season when the intensity drops and performance is less of a concern. In season, I'd be more cautious, especially around match day and heavy training days where you need to be fuelled properly.

Low Carb Diets

What is it?

Low carb sits somewhere between a normal diet and keto. You're reducing carbohydrates significantly but not necessarily going to the extreme of ketosis. There's no strict definition but most low carb approaches aim for somewhere between 50 and 150 grams of carbs per day, compared to the typical Western diet that might have 250 to 300 grams.

Think cutting out bread, pasta, rice, cereals, and sugary foods, but maybe still having some oats, some fruit, and root vegetables.

How does it work?

Lower carbs mean lower insulin, which again creates an environment more conducive to fat burning. You also tend to eat more protein and fat on a low carb approach, both of which are more satiating than carbs gram for gram.

A well-known NIH study led by Kevin Hall compared low-fat and low-carb diets in a controlled metabolic ward setting. Both groups lost weight, and interestingly body fat loss was actually slightly greater in the low-fat group when calories were matched, (Hall et al., Cell Metabolism, 2015, as reported in ScienceDaily 2015) though the low-carb group lost more total weight initially due to water loss from glycogen depletion.

A separate review in the Journal of Nature and Science of Medicine confirmed that when calorie intake is matched between low-carb and low-fat diets, no significant difference in weight loss is observed, (JNSM, 2025) which again points to total calorie intake as the primary driver.

Does it work?

Yes. Cutting carbs tends to naturally push people into a calorie deficit because it removes a lot of the hyperpalatable, easy-to-overeat foods from the diet. You're less likely to sit there eating six slices of toast or half a bag of crisps if you're on a low carb approach.

A lot of people also feel less bloated on lower carbs, particularly around refined carbs and processed foods. Some of that is water retention dropping, some is just better food quality overall.

Should a GAA player go low carb?

Same principle as keto. Be careful in season. Carbs are your friend for performance. If you're looking to lean out in the off season, a moderate reduction in carbs is one of the easier ways to naturally drop your calorie intake without tracking every single thing.

But I always say, if you are going to cut carbs, make sure you're still eating enough protein to protect your muscle mass, and that you're timing any remaining carbs around your training sessions. Don't be cutting carbs on a night where you have a hard training session the next morning.

Low Fat Diets

What is it?

Low fat has been around since the 1980s and got a bit of a hammering in recent years because the food industry went wild producing low fat products that were full of sugar to compensate. But the principle itself isn't bad.

A low fat approach means reducing dietary fat intake, typically aiming for fat to make up less than 30% of total calories, and sometimes significantly less on a very low fat plan.

How does it work?

Fat is the most calorie-dense macronutrient at 9 calories per gram, compared to 4 calories per gram for both protein and carbohydrates. So reducing fat intake is one of the more efficient ways to create a calorie deficit without having to eat tiny portions. You can eat a decent volume of food and still be in a deficit.

The issue is that fat is important for hormone production, joint health, brain function, and absorbing fat-soluble vitamins. Going extremely low fat for a prolonged period isn't something I'd recommend for any active person.

Does it work?

The Hall et al. metabolic ward study found that dietary fat restriction resulted in greater measured body fat loss than carbohydrate restriction (Hall et al., Cell Metabolism, 2015) when calories were controlled. So in a tightly controlled setting, low fat has the edge on pure fat loss. In the real world, it comes down to which approach you can stick to.

What tends to happen is that low fat plans fail people not because the approach is wrong, but because the food choices are boring and the low fat processed food alternatives are full of sugar and end up spiking hunger. Pick whole foods, reduce added fats where you can, and you'll see results.

High Protein Diets

What is it?

This one doesn't get its own trendy name but it's probably the most evidence-backed approach for active people. Eating a high protein diet, typically above 1.6 grams per kilogram of bodyweight and often up to 2.2 grams or more, while keeping overall calories in a deficit.

How does it work?

Protein does a few useful things. First, it's the most satiating macronutrient. It keeps you fuller for longer, which naturally reduces how much you eat. Second, it has the highest thermic effect of food, meaning your body actually burns more calories digesting protein than it does digesting fat or carbs. Third, and most importantly for any GAA player, it protects muscle mass when you're in a calorie deficit.

If you're cutting calories without eating enough protein, a significant portion of the weight you lose could be muscle rather than fat. That's bad for performance, bad for body composition, and bad for long-term metabolism.

Should a GAA player prioritise protein?

Yes. Without question. Whatever approach you take to eating, make sure your protein intake is sorted first. For an 80 kilo player, that means aiming for at least 130 to 160 grams of protein per day. Get that right, keep calories appropriate for your goals, and the rest is just personal preference.

Protein from whole food sources first. Chicken, beef, eggs, Greek yogurt, fish, cottage cheese. Protein powder as a supplement when whole food isn't practical, like post-training or on the road. But food first, always.

They All Come Back to the Same Thing

Look, here's what nobody online wants to say because it's not exciting content. All of these approaches work when they help you eat fewer calories than you burn. None of them work when they don't.

Keto might help you eat less because the high fat and protein keeps you satisfied. Intermittent fasting might help you eat less because you've shrunk your eating window. Low carb might help you eat less because you've cut out the hyperpalatable processed stuff. High protein might help you eat less because protein is filling.

Same destination. Different roads.

This is backed up consistently in the research. As one review put it, an energy deficit is the most important factor in weight loss, (PMC8017325, Kim & Bae, 2021) with macronutrient composition being secondary when calories are controlled.

The best approach for fat loss is the one you can actually stick to. If you hate eating fat and the thought of a keto diet makes you want to pack it in, then keto is not the best approach for you regardless of what any YouTube video says. If skipping breakfast causes you to be ravenous by 11am and you end up absolutely destroying your lunch, then 16:8 fasting probably isn't your best tool.

Find what fits your life, your training, your food preferences, and the demands of your GAA season. Build a calorie deficit that's manageable and sustainable. Hit your protein. Sleep well. Train hard. That's the job.

What This Looks Like in Practice

Here's how I'd think about it as a club GAA player:

Brasse, P., Zerdka, J., Staszkiewicz, K., et al. (2025). Intermittent Fasting: Efficacy, Safety, and Its Impact on Body Weight, Glucose Metabolism, and Gut Microbiota. Cureus. DOI: 10.7759/cureus.97773. PMC12740946.

Gu, L., Fu, R., Hong, J., et al. (2022). Effects of Intermittent Fasting in Human Compared to a Non-intervention Diet and Caloric Restriction: A Meta-Analysis of Randomized Controlled Trials. Frontiers in Nutrition. DOI: 10.3389/fnut.2022.871682. PMC9108547.

Hall, K.D., Bemis, T., Brychta, R., et al. (2015). Calorie for Calorie, Dietary Fat Restriction Results in More Body Fat Loss than Carbohydrate Restriction in People with Obesity. Cell Metabolism. 22(3), 427-436. As reported in ScienceDaily, August 2015.

Kim, J.Y., & Bae, J.H. (2021). Optimal Diet Strategies for Weight Loss and Weight Loss Maintenance. Journal of Obesity & Metabolic Syndrome. PMC8017325.

Malinowska, M. (2024). Ketogenic Diet: A Review of Composition Diversity, Mechanism of Action and Clinical Application. Journal of Nutrition and Metabolism. DOI: 10.1155/2024/6666171.

Masood, W., et al. (2022). Ketogenic diet for human diseases: the underlying mechanisms and potential for clinical implementations. Signal Transduction and Targeted Therapy. Nature Publishing Group.

Mayo Clinic. (2024). Counting calories: Get back to weight-loss basics. Retrieved from mayoclinic.org/healthy-lifestyle/weight-loss.

Sackner-Bernstein, J., Kanter, D., & Kaul, S. (2015). Dietary Intervention for Overweight and Obese Adults: Comparison of Low-Carbohydrate and Low-Fat Diets. A Meta-Analysis. PLoS ONE. 10(10): e0139817.

Zhang, Q., Zhang, C., Wang, H., et al. (2022). Intermittent Fasting versus Continuous Calorie Restriction: Which Is Better for Weight Loss? Nutrients. 14(9):1781. PMC9099935.

Journal of Nature and Science of Medicine. (2025). Low-fat versus Low-carbohydrate Diet. JNSM. doi:10.4103/jnsm.jnsm.

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