So You Want To Know More About Fasting
Is intermittent fasting a metabolic loophole? A biohack that tricks your body into burning fat faster? Spoiler: no. Fasting isn't magic, and it doesn't change the basic rules of fat loss. But that doesn't mean it's useless. We're breaking down what fasting actually does in your body, why people think it works, when it might be helpful, and when it's likely to backfire. Plus, we'll tell you exactly who should avoid fasting altogether (hint: if you're training for performance, this probably isn't for you).
BLACK IRON RADIO EP. 316: So You Want To Know More About Fasting
Fasting gets marketed as a metabolic shortcut, a biohack, or a way to "trick" your body into burning fat. Reality check: it's none of those things.
Morgan and Sabrina break down what fasting actually is (and isn't), how it affects blood sugar, insulin, glycogen, and fat use, and why burning fat isn't the same thing as losing body fat. They dig into why fasting can feel good for some people, where the perceived benefits often come from, and how hunger hormones adapt to eating windows over time.
The conversation also covers when fasting can backfire (especially for athletes, high-stress humans, and anyone with performance goals) and why calorie balance, training quality, and sustainability matter far more than meal timing rules.
No hype, no fear-mongering. Just physiology, context, and honest nuance so you can decide what actually makes sense for you.
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Fasting. It's everywhere right now. Your coworker swears by it, your favorite influencer posts about their fasting window, and maybe you've wondered if you're missing out on some metabolic magic trick. Let's cut through the noise and talk about what fasting actually is, how it works (and doesn't work), and whether it's right for you.
Spoiler alert: Fasting is not a metabolic loophole. It's not a biohack. It's not tricking your body into burning a specific type of fuel. But that doesn't mean it's useless either.
What Actually Is Fasting?
Intermittent fasting means limiting the times of day you're eating food. The most common approach is a 16:8 split (16 hours fasting, 8 hours eating), but some people do 12:12 or even more extreme windows. To technically count as fasting, you need a minimum 12-hour period without consuming food.
That's it. You're not doing anything magical. You're just condensing when you eat.
The Biology: What's Actually Happening
When you stop eating, your blood sugar declines and your pancreas lowers insulin output. Insulin's job is to move nutrients from food into your cells for storage. When insulin is low, your body starts pulling from stored energy instead of incoming food.
Here's where people get excited. They hear "you'll burn fat during fasting" and think that means automatic fat loss. Not quite.
Your body has two main fuel sources: glycogen (stored carbs in your liver and muscles) and fat. When you're not eating, your body burns through glycogen first. Once that's depleted, it moves to fat. But burning fat for energy is not the same thing as losing body fat. You can burn fat all day long and still be over-consuming calories, putting everything right back into storage.
The only way to lose body fat is a caloric deficit. Period. Your total calories in must be less than your total calories out over time. Fasting doesn't change that equation. It might make it easier to create a deficit (smaller eating window = less opportunity to overeat), but the deficit itself is still doing the work.
Why People Think Fasting Works
There are real reasons people see results with fasting, but it's usually not what they think:
Fewer calories without trying: When you only have a 6-hour window to eat, you're probably consuming less overall. It's harder to overeat when you have limited time.
More consistency: Having clear rules about when you can and can't eat removes a lot of decision fatigue. You're not saying no to the breakroom donuts or yes to the drive-thru as often because you're simply not eating during those times.
The "new diet" effect: When you start any new eating plan, you tend to pay more attention to everything. You drink more water, you add vegetables, you go for walks. The fasting gets credit, but really it's all those other lifestyle improvements working together.
Mental clarity: Some people report feeling sharper during fasting. This might be psychological (the pride of successfully completing your plan), or it could be the norepinephrine release that happens when your body is in a mild stress state. Your body thinks it needs to be alert to find food, so it releases adrenaline. That can make you feel awake and focused, but it's also a survival mechanism. Not necessarily "healthy" long-term.
Feeling lighter: There's literally less food mass in your digestive system. You might also be retaining less water if you're inadvertently eating less sodium. These are real physical sensations, but they're not fat loss.
Your Hunger Hormone Is Smarter Than You Think
One interesting thing about fasting is how it affects ghrelin, your hunger hormone. You know that feeling when you're absolutely starving, then 15 minutes later you're fine? That's ghrelin being adaptive.
When your body sends a hunger signal and you don't respond, it doesn't keep screaming at you forever. After about 20 to 40 minutes, it says "okay, food isn't available right now" and backs off. This is why people can train themselves to not be hungry during their fasting windows. Your body adjusts to the pattern you create.
This can be helpful for building awareness. Are you actually hungry, or is it just routine? Do you always snack at 4pm whether you're hungry or not? Fasting forces you to evaluate what's real hunger versus boredom or habit.
When Fasting Might Actually Help
Let's be honest about when fasting can work:
If you struggle with late-night snacking: Setting a hard cutoff time (like "no food after 7pm") can help break that pattern.
If you prefer fewer, larger meals: Some people just don't like eating small amounts throughout the day. If you'd rather eat two bigger meals in a shorter window, go for it.
If it fits your lifestyle: Maybe you're not hungry in the morning anyway and naturally don't eat until 11am. Great! That's already a 13-14 hour fast if you stop eating by 10pm.
If you like clear rules: Some people thrive with structure. Having set eating windows removes ambiguity and decision fatigue.
The key is that fasting is a tool for creating a caloric deficit or managing your eating patterns. It's not doing anything your body wouldn't do otherwise if you ate the same calories spread throughout the day.
When Fasting Backfires
Here's where things get messy:
Massive eating sessions: If you're cramming all your calories into a 6-hour window, you're probably going to feel terrible. That's a lot of work for your digestive system, and you're likely not getting quality, balanced meals.
Your body adapts: If you consistently undereat, your energy expenditure can down-regulate. You'll have less energy, move less throughout the day, and your workouts will suffer. That initial progress plateaus because your body is conserving energy.
Training quality tanks: If you're someone who works out at 6am but you're not eating for a 12-hour window, good luck getting a quality training session in. You'll be dragging. Your performance matters, and under-fueled training is a recipe for poor results and potential injury.
Sleep suffers: Being hungry, having low energy, and dealing with the stress of restriction can all impact sleep quality. And poor sleep makes everything worse.
Micronutrient density drops: When you have less time to eat and you're dealing with intense cravings, the odds of choosing nutrient-dense foods go down. You're more likely to reach for whatever sounds good in the moment rather than a balanced meal with vegetables and variety.
Protein becomes a nightmare: Need 150 grams of protein in a 6-hour window? Have fun with those four protein shakes and three cans of tuna. Now you have mercury poisoning and won't poop for five days. Not exactly the point of eating.
Disordered eating patterns: Anytime you add strict rules about when you can and can't eat, you're on tricky ground. For anyone with a history of disordered eating or who's prone to obsessive food rules, fasting can become problematic quickly.
Fasting and Training: A Bad Match
If you're training for performance, fasting is probably not your friend. Performance athletes need to eat before, during, and after training sessions. Those are the most important eating windows of the day.
If you're trying to get stronger, build muscle, train for a weightlifting meet, or PR your lifts, being under-fueled during training is counterproductive. You'll be more injury-prone, you won't lift as heavy, and your recovery will suffer.
Now, if your training goals are more casual (just moving your body, getting some zone 2 cardio), fasting might not interfere much. But if you have specific performance goals, ask yourself: is fasting more important than getting what I want out of my training?
You can work around it to some degree. Maybe your morning session is light movement and you save your heavy lifting for later in the day during your eating window. But it takes planning and awareness, and honestly, it's adding complexity that might not be worth it.
Who Should NOT Fast
High-stress individuals: If you're already struggling with chronic stress and not managing it well, adding the stress of a caloric deficit (which fasting often creates) is not helpful. You probably just need to focus on eating enough and regulating stress.
Performance athletes: If you have specific training goals that require strength, power, or endurance, fasting will likely interfere with your progress.
Anyone with a history of disordered eating: Putting yourself in a restrictive box with strict eating rules is a bad idea if you've struggled with food issues in the past. The rigid structure can trigger unhealthy patterns.
The Bottom Line on Fasting
Fasting doesn't change how fat loss works. Two people in the same caloric deficit will lose weight at the same rate whether one is fasting for 16 hours and the other is eating normally throughout the day. In fact, the non-fasting version is probably more sustainable.
That said, if fasting interests you and you think it might fit your lifestyle, there's no harm in trying it for a couple weeks and seeing how you feel. Just don't expect magic. And definitely don't fall for the marketing that claims fasting is a metabolic hack or a shortcut to fat loss.
If you try it and it works for your schedule, you're hitting your protein goals, you feel good, and your training isn't suffering, cool. Stick with it. But if you're constantly hungry, irritable, your workouts suck, and you're not seeing results, it's okay to stop. Sustainability matters more than any single strategy.
The real magic? Hiring a nutrition coach who can help you find what actually works for you. Not what works for the influencer you follow, not what worked for your friend's dad. What works for YOUR body, YOUR lifestyle, and YOUR goals.
We're happy to help you figure that out.
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If you enjoyed this conversation, check out more episodes of Black Iron Radio, where we cut through the noise and give you real, no-BS advice on feeling, performing, and looking your best. Each week we share practical nutrition, training, and wellness strategies and tips to help you succeed.
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