Myths and Misunderstandings About Fat Loss

There’s a lot of confusion around fat loss, and to be fair, the science can be genuinely tricky to interpret. Some of it’s technical. Some of it’s conflicting. And, let’s be honest, some of it gets overhyped by people selling simple solutions.

I think part of the reason diet myths are so appealing is that they sound straightforward. You hear things like: “Insulin is the real problem,” or “Just fast and you’ll lose weight,” or “Cut carbs – they’re the enemy.” These ideas catch on because they make it all seem so simple. Like there’s one main reason you’re not losing fat, and one obvious way to fix it.

And honestly, when progress feels slow or confusing, that kind of certainty is comforting. You start thinking, maybe I’ve just missed something obvious.

This article actually came out of a recent conversation with a close friend – someone I trust and whose opinion I really value. We were going back and forth on some of these common beliefs, and it struck me how easily even well-informed people can get pulled off track on this topic.

It’s not always about misinformation. Sometimes it’s just the hope that there’s a simpler explanation. That there’s one thing you’ve overlooked – and if you could just fix that, everything else would fall into place. When its proving to be a real struggle tp shed some pounds, that kind of thinking is hard to resist. It makes the more complex, less satisfying truths easier to ignore.

So let’s look at three of the most persistent fat loss myths. Not to nit-pick every theory, but to add some perspective, and hopefully help you avoid wasting time or effort on the wrong things.

Myth 1. “Insulin spikes cause fat gain”

This is a very common misconception. The argument goes something like this: insulin is a storage hormone, and it stops fat burning. High-carb meals spike insulin… so carbs must make you fat. Therefore, don’t eat carbs.

It sounds logical. But that’s not quite how it works.

Yes, insulin promotes nutrient storage. That’s its job. It helps move glucose and amino acids into your cells. And yes, it does temporarily reduce fat breakdown. But the idea that this, on its own, causes fat gain doesn’t hold up when you look at the full picture.

Let’s zoom out. If two people eat the same number of calories and get the same amount of protein, it really doesn’t matter much whether most of those calories come from carbs, protein or fat – at least not in terms of body fat loss.

What does matter, and this comes through in study after study, is overall energy balance. How much you’re eating versus how much you’re using. That’s the core. Not the exact shape of your insulin curve after lunch.

There’s a study by Hall et al. (2015) that found people actually lost more fat on a higher-carb, lower-fat diet – which triggered more insulin – than on a lower-carb diet with the same number of calories. If insulin spikes caused fat gain directly, that result wouldn’t make sense.

Also, protein spikes insulin too. Whey protein in particular causes a strong insulin response. But no one’s worried about a chicken breast making them fat. So if we’re going to blame insulin, we’d need to apply that logic across the board, and it quickly falls apart.

And while we’re here, it’s worth touching on another common claim – that insulin spikes make you hungrier. That’s not what we see in the research. In fact, insulin actually plays a role in promoting satiety. It helps signal to the brain that you’ve eaten and don’t need more food. So a healthy rise in insulin after a meal is part of what reduces appetite, not what drives you to raid the fridge an hour later.

That’s not to say insulin doesn’t matter. It does. But the fact that insulin rises after meals isn’t a problem – it’s normal. It only becomes an issue when insulin levels are pathologically or chronically elevated, usually as a result of long-term overeating and inactivity. Not when it spikes briefly after a meal.

Myth 2. “You need to be in ketosis to lose fat”

Ketosis gets a lot of attention. And honestly, I can see why. For some people, drastically reducing carbs makes things feel simpler. Fewer choices, fewer cravings, and often, less overall food. That can definitely lead to fat loss.

But this is where things get murky. It’s easy to look at those results and assume that being in ketosis is what’s driving the fat loss, when in reality, it might just be that people are eating fewer calories overall. It’s important not to confuse correlation with causation.

When you're in ketosis, your body starts producing ketones, which are a kind of backup fuel source it uses when carbs are scarce. It’s a shift in fuel preference. Not a metabolic magic trick.

Yes, fat oxidation increases in ketosis. But fat oxidation isn’t the same as fat loss. You can be burning more fat in the moment, while still gaining fat overall – if you’re in a calorie surplus. What matters is your net fat balance over time.

And your body is constantly switching between different fuel sources anyway, depending on things like activity level, what you’ve eaten, time of day, and so on.

In another study by Hall et al. (2016), participants on a ketogenic diet did burn more fat, but they actually lost slightly less body fat compared to when they ate a higher-carb diet with the same number of calories and protein. That’s worth thinking about.

This doesn’t mean keto doesn’t work. It clearly can – for some people. But usually, it works because it helps them eat less, not because ketones have some special fat-burning property.

Myth 3. “Intermittent fasting is optimal for fat loss and muscle retention”

I’ve used intermittent fasting myself at times. You might have too. It can be really helpful for managing food intake and staying consistent with your eating habits. If it helps you eat fewer calories without much thought or effort, that’s great.

But when it comes to keeping muscle – or building it – fasting comes with trade-offs that are easy to overlook.

Muscle protein synthesis (MPS), the process your body uses to repair and grow muscle, is mainly triggered by two things: strength training and protein intake.

You don’t need to graze all day long, and no one is suggesting you set a timer to eat every two hours. But ideally, you want to give your body a few solid signals throughout the day. Roughly every 3 to 5 hours, with a decent hit of protein. That seems to keep the muscle-building machinery running, or at least nudged in the right direction.

With intermittent fasting, especially if your eating window is only 6 or 8 hours, you’re often only getting one or two real meals. That means fewer opportunities to spike MPS. And if you’re also in a calorie deficit – as most people are when trying to lose fat – that’s already a tougher environment for muscle retention.

There’s a study by Areta et al. (2013) that compared the same total protein intake spread across multiple meals versus fewer, larger meals. The more frequent, evenly spaced meals led to significantly greater MPS.

So even if you’re hitting your daily protein target, how you distribute it still matters – maybe more than people realise.

There’s also the issue of anabolic signalling, especially the mTOR pathway, which is central to muscle growth. Prolonged fasting suppresses mTOR activity, partly through AMPK signalling. That’s not always bad – sometimes you do want to prioritise things like cellular repair – but if your main goal is holding onto lean mass while dieting, it’s not ideal.

Another study (Pasiakos et al., 2010) found that even with high protein intake, MPS dropped during a 40% energy deficit. So if you’re fasting, under-eating, and not spacing your protein out well… the risk of losing muscle goes up.

So, what actually matters?

After trying most of these approaches myself – and going down a few rabbit holes I probably didn’t need to – this is where I’ve landed.

If your goal is to lose fat and keep your muscle, the basics are still the foundation:

• Stay in a calorie deficit – but make sure it’s one you can actually stick to.
• Eat enough high-quality protein (1.6–2.2 g/kg/day is a good place to start).
• Lift weights – progressively and consistently. Your weights program doesn’t have to be fancy – it just has to challenge you.

You don’t need to cut carbs. You don’t need to chase ketones. And you don’t need to fast for 16 hours a day (unless that genuinely works for you!).

Insulin isn’t the villain. Ketosis isn’t the secret. Fasting isn’t the shortcut.

They’re all just tools. Use them if they help. Set them aside if they don’t.

And above all, try to look at the bigger picture. What you can stick to, recover from, and enjoy – most of the time – will always beat the perfect-sounding plan that burns you out by week three.

References

1. Hall KD, Chen KY, Guo J, Lam YY, Leibel RL, Mayer LE, et al. Energy expenditure and body composition changes after an isocaloric ketogenic diet in overweight and obese men. Proc Natl Acad Sci U S A. 2016;113(27):8161–6.
2. Hall KD, Bemis T, Brychta R, Chen KY, Courville A, Crayner EJ, et al. Calorie for calorie, dietary fat restriction results in more body fat loss than carbohydrate restriction in people with obesity. Cell Metab. 2015;22(3):531–42. 
3. Areta JL, Burke LM, Ross ML, Camera DM, West DW, Broad EM, et al. Timing and distribution of protein ingestion during prolonged recovery from resistance exercise alters myofibrillar protein synthesis. J Nutr. 2013;143(4):386–91. 
4. Pasiakos SM, Vislocky LM, Carbone JW, Altieri N, Konopelski K, Freake HC, et al. Acute energy deprivation affects skeletal muscle protein synthesis and associated intracellular signaling proteins in physically active adults. J Nutr. 2010;140(4):745–51. 
5. Pasiakos SM, Cao JJ, Margolis LM, Sauter ER, Whigham LD, McClung JP, et al. Effects of high-protein diets on fat-free mass and muscle protein synthesis following weight loss: a randomized controlled trial. Am J Clin Nutr. 2013;98(3):511–9. 
6. Glynn EL, Fry CS, Drummond MJ, Dreyer HC, Dhanani S, Volpi E, et al. Muscle protein breakdown has a minor role in the protein anabolic response to essential amino acid and carbohydrate intake following resistance exercise. Am J Physiol Regul Integr Comp Physiol. 2010;299(2):R533–40. 

About the author

Marc Barton is a Brazilian Jiu Jitsu black belt, educator, and former doctor with a background in human physiology and medicine. He holds a BSc in Physiology and an MBBS medical degree, and spent over a decade working on the frontline in emergency and intensive care medicine. 

Now teaching Jiu Jitsu full time as the head instructor at Kingston Jiu Jitsu, Marc brings a rare blend of scientific depth and real-world experience to his coaching. His approach focuses on biomechanics, skill progression, and longevity – especially for those training into their 30s, 40s, and beyond.