The Advantages of a High-Carb/Low-Fat Diet

Welcome back to our two-part series that seeks to redeem a much-maligned macronutrient: carbohydrates.

In our previous article, we took a look at the pervasive idea that carbs in and of themselves make you fat and highlighted research which shows that instead, it’s excess calories — whether they come from fat, carbs, or protein — that packs on the pounds.

It’s entirely possible to lose body fat while eating a high-carb/low-fat diet. As long as you’re burning more calories than you’re consuming, you’re going to lose weight.

It’s also definitely possible to lose weight on a high-fat/low-carb diet, though the reason isn’t that there’s something magic about fat or evil about carbs: high-fat/low-carb diets just tend to lead people to eat fewer calories thanks to limited food choices.

So if the macronutrient breakdown doesn’t matter when it comes to losing weight, is there a reason to choose one diet over the other?

There is, depending on your activity level. For active individuals who work out hard and participate in things like weight lifting, running, or CrossFit, a low-fat/high-carbohydrate diet can greatly enhance their athletic performance and recovery from exercise. Below, we dig into the details as to why.

Understanding How Your Body Gets Power: The 3 Metabolic Pathways

Before we get into the performance benefits of carbohydrates, we need to understand how our body gets the power it needs to function and move. You probably learned a lot of this stuff in high school biology. In case you’ve forgotten or were busy drawing those cool “S” things on your folder while your teacher was explaining metabolic pathways, consider this your review.

Your body transfers energy via a molecule called adenosine triphosphate, or ATP. When a cell needs energy, ATP is broken down by removing a phosphate group from the ATP molecule. This break down releases energy and gives the cell the power it needs to do what it needs to do to ensure your carcass keeps living and moving. All of your body’s cells use ATP for energy — blood cells, liver cells, bone cells, nerve cells, brain cells, muscle cells. If it’s a cell and living, it uses ATP.

When ATP loses one of its three phosphate groups, it becomes an adenosine diphosphate molecule since it only has two phosphates attached to it. ADP doesn’t have readily available energy bound up in it, so the body needs to recycle it back into ATP by adding another phosphate to it. It does this through three metabolic pathways:

1. Phosphagen. This pathway can create ATP really fast because it relies on stored creatine phosphate in the muscles. The creatine phosphate molecule merely needs to transfer its phosphate to the ADP to reconstitute into ATP.

When you’re taking part in intense activities that last for just a few seconds, you’re primarily relying on your phosphagen metabolic pathway to get the ATP your muscles need. An excellent example of this would be performing a single, one-rep weight lifting max.

2. Anaerobic. After your muscles have used up all of their stored ATP and creatine phosphates, it starts creating ATP from stored glycogen in your muscles. Remember from our previous article that glycogen is how our muscles store glucose. Our muscles get glycogen from . . . carbohydrates.

Anaerobic glycolysis contributes to a process that creates two ATP molecules from a single glucose molecule. While that might not seem like a lot, because anaerobic glycolysis doesn’t require oxygen to produce ATP, it can go through several cycles to form new ATP very quickly. Besides ATP, anaerobic glycolysis creates lactic acid as a waste product.

Your muscle cells primarily use anaerobic glycolysis for intense activities lasting 30 seconds to two minutes. A sprint, a set of five while lifting weights, or running up and down a basketball court are good examples of activities that primarily rely on anaerobic glycolysis to create ATP.

3. Aerobic. This metabolic pathway is an ATP producing powerhouse. Unlike phosphagen that can only use creatine phosphate to create ATP or anaerobic glycolysis that can just use glucose to generate ATP, aerobic respiration can use glucose and fatty acids (which we get from the fat we consume or the fat we have stored around our belly). So aerobic respiration is versatile.

What’s more, aerobic respiration creates a crap-ton of ATP. When our aerobic metabolic pathway uses glucose to generate ATP, it can contribute to producing 36 ATP from a single glucose molecule. When it uses fatty acids, it can contribute to creating 106 ATP. From this perspective, aerobic respiration is much more efficient.

But there’s a catch: aerobic respiration requires oxygen to create ATP, which makes the process take longer.

First, it takes a bit for oxygen to even get to your muscle cells to begin aerobic respiration. It’s not super slow, but in the time it takes oxygen to get to your muscle cells to even start making ATP, your muscles could already be creating ATP with either your phosphagen pathway or anaerobic pathway because those don’t require oxygen.

Second, even when oxygen gets to your muscle cells, it has to go through a few more chemical processes to create ATP compared to anaerobic glycolysis.

Because aerobic respiration has such a relatively slow rate of ATP production, your muscle cells use it during longer duration, lower intensity activities. For example, as you’re sitting here reading this article, your body is primarily using its aerobic pathway. When you take a hike, you’re mainly using the aerobic metabolic pathway. When you jog at a steady, moderate pace, you’re primarily using your aerobic pathway.

It’s important to keep in mind that all three pathways are going at the same time. You’re never not using any of them; you’re never purely in anaerobic mode, or purely in aerobic mode. You just might rely on one pathway more depending on what you’re doing.

The (Advantageous) Effect of Carb Intake on Various Kinds of Physical Activity

Now that we have a basic understanding of how our muscles get the energy they need to contract, we can start to see why carbs can play an important role in athletic performance. The magnitude of this role depends on the type/intensity of the physical activity, and thus the degree to which it utilizes one of the 3 processes outlined above in order to generate power/effort/stamina. As we’ll see though, all of them ultimately rely on carbs for maximum performance.

Weight Lifting

Let’s say you decide to go low-carb while continuing to do barbell training. Your typical workout consists of three lifts, and you’re doing three sets of five at 80% of your 1 rep max. Basically, these are hard training sessions.

Your first workout while eating low-carb will actually go pretty well. Why? Because weight lifting largely utilizes anaerobic glycolysis to produce power and you likely have a lot of stored glycogen in your muscles from before you started stripping the carbs from your diet. So you think to yourself “Man, low-carb is awesome! I’m going to lose weight, and my performance still feels great!”

But by the end of the training session, you’ve used up a good chunk of that stored muscle glycogen. Not all of it, but a decent amount.

You have a rest day on Tuesday and eat very few carbs. Glycogen stores weren’t replenished that much.

You come back to the gym on Wednesday. The first set of squats feels good, but that’s because you were likely using stored ATP and creatine phosphate in your muscles for your energy. The second set feels a bit heavier, but not terrible. You’re now using anaerobic glycolysis. The third set feels even harder because you’re using up more of your depleted reserves of stored glycogen. By the end of the workout, you feel drained.

You rest on Thursday and continue to eat very few carbs. Glycogen stores deplete even further.

You come back to the gym on Friday. First rep on your squats feels okay. Again, you’re just using stored ATP and creatine phosphate for that one. The second rep feels like you’re going to die, but you finish it. Same with your third rep. You manage to complete the set, but feel completely drained. You’ve likely reached the dregs of your stored glycogen. You start the second set of squats and go down to the bottom. You stay at the bottom of the squat. You just don’t have it in you to lift the bar. Because you’re taking part in an anaerobic activity, your body needs glucose to create the ATP it needs. But because you’ve been eating low-carb, your body doesn’t have a supply of glucose to replenish your ATP.

So you reduce the weight on the bar so you can finish your workout. You feel like garbage at the end.

You continue to eat low-carb through the weekend. Consequently, glycogen stores are hardly replenished. You hit the gym again on Monday. The first rep of the prescribed weight feels really heavy. You realize this is going to be another terrible workout. And it is.

As my nutrition coach, Robert Santana, says about low-carb diets and weight training, “Things start off pretty well, but quickly go to hell.”

If you’re doing low-rep sets (like 1-3 reps) and you give yourself plenty of rest between sets, you can probably get away with eating low-carb. It won’t help, but it won’t hurt you that much. With those low reps, you’re primarily using your phosphagen metabolic pathway and won’t be dipping into your glycogen stores.

The problem with low-rep training is that it’s hard to get stronger with low reps as you become more and more advanced in your training. You’ll need volume to do that. And to be able to complete the volume necessary for adaptation, you’ll be back to needing carbs.

Bottom line: To get stronger, and be able to push yourself in the gym, a diet high in carbs is crucial. 

High Intensity/CrossFit-Type Training

High intensity workouts like HIIT or CrossFit are even more anaerobic — and glycogen depleting — than weight lifting. Just two 30-second sprints will deplete your glycogen stores nearly by half.

If you want to be able to generate enough power to sprint like crazy, do a bunch of a box jumps, hit the heavy bag, and so on, you’ll be greatly benefited by eating a high-carb diet.

Several studies have borne this out. For example, time to exhaustion when doing high-intensity exercise is much longer on a high-carb diet, compared to a high-fat diet; i.e., a high-carb diet allows you to train harder for longer. That’s because a high-carb diet ensures your muscle cells are fully stocked with glycogen that can quickly be turned into ATP during an intense training bout.

Jogging/Running or Other Types of Aerobic Exercise

Carbs have a lesser role in longer duration, lower intensity activities, because these rely more on aerobic respiration to create ATP, which is fueled by both glucose and fat.

This is borne out by research. The most cited study by low-carb proponents as evidence for the viability of the diet for athletic performance was conducted by Stephen Phinney back in 1983. He took five well-trained male cyclists and put them on a zero-carb diet for four weeks. This was a strictly controlled study, so Phinney and his researchers made sure these cyclists were truly eating keto.

Glycogen stores went down as a result of being on a ketogenic diet. What happened to the athletic performance of these cyclists as a result?

Before the keto diet, Phinney had the five cyclists ride at 62%-64% VO2 max for as long as they could. So not too hard. This is a VO2 max range in which our muscle cells are largely using fat for energy through aerobic respiration.

Before switching to a ketogenic diet, the cyclists lasted, on average, just under 150 minutes at that pace. After four weeks on the ketogenic diet, they lasted, on average, about the same amount of time at that same pace.

It would seem from this finding that high-fat/low-carb diets don’t hurt aerobic endurance activities, and runners, cyclists, and triathlon athletes can skip the carbs, and still perform well.

But this conclusion comes with some important caveats.

If you take a closer look at each individual in the Phinney study, the results actually varied dramatically. On average, performance didn’t suffer among the five cyclists, but averages can be deceiving. Two of the subjects actually performed better on a ketogenic diet. Two of the subjects got worse. One guy’s performance didn’t change at all.

So results vary with a low-carb diet: For some people it can help, for others, it can hurt. And for some, it might not do anything.

Further, while there’s a non-guaranteed chance that a low-carb diet could improve your performance in long-duration/low-intensity activities, that’s only the case if you stay 100% in aerobic mode.

Remember, this study had the cyclists going at just 62%-64% VO2 max. That’s not going super hard. Another rubric out there for staying in aerobic mode is keeping your heart rate around 180 minus your age. If you’ve ever tried to run at that pace, you’ll know you have to practically crawl, and even periodically full on stop and walk. And those are just training runs. Forget about keeping your heart rate that low on race day; no endurance event has an athlete running at a pace that would keep them in aerobic, fat oxidation mode for the entire race. All endurance sports would actually be better termed “intermittent intensity sports,” as 5Ks, triathlons, and even ultramarathons all have periods where an athlete is going all out at 80-95% VO2 max. That’s how you run competitively. You grind up hills; you turn on the jets to pass a competitor; you kick at the end. You run fast. And when you run fast, you can no longer use fat for ATP; you go anaerobic and start burning glucose.

Phinney, in fact, later admitted that while the low-carb diet of the cyclists in his study hadn’t hurt their aerobic performance, it had negatively impacted their ability to sprint.

That’s why there’s no published evidence that low-carb/high-fat diets help endurance athletes give competition-level, high-intensity effort. The studies instead show that such a diet typically hurts performance when an athlete goes above 70% VO2 max (which again happens pretty much anytime you’re racing to win).

That’s also why the number of elite distance athletes on a low-carb diet is close to non-existent. The vast majority of top competitive athletes do quite the opposite. For example, studies on elite Kenyan runners, who have netted many a running title, show they consume between 441-607 grams of carbohydrates a day — over 76% of their daily calories.

Bottom line: If you’re a runner or cyclist who plans on staying only in an aerobic zone — never grinding up a hill, or sprinting, or entering a competitive event — then the low-carb diet might work okay for you. But if you ever plan on going fast, or racing, or pushing yourself in any way, then you’re going to need the kick that comes from carbs.

But Won’t Performance Improve Once You Become “Fat-Adapted”?

Low-carb advocates will admit that athletic performance initially suffers when you make the switch from a high-carb diet to a low-carb one. They’ll even argue that there wasn’t a more consistent improvement in Phinney’s cyclists, because they weren’t yet fat-adapted.

Once you do get fat-adapted, say these folks, performance will bounce back because your body will be able to utilize fat more quickly to replenish ATP. You’ll be able to lift weights with the same power and run forever without bonking.

First, tests were done on Phinney’s cyclists which showed that they were indeed thoroughly fat-adapted. So that wasn’t the issue. But their sprinting ability still suffered; in fact, the cyclists who were the most keto adapted were the ones whose sprinting performance deteriorated the most. No matter how fat adapted you get, anaerobic activities fueled by fat don’t have as much power as those fueled by carbs. Yes, you can run a long time, at a moderate pace, without refueling, but when you need to sprint, you’re going to feel absolutely empty.

Second, while fat-adaption has some advantages for aerobic exercise, it also comes with trade-offs that negate these benefits, as well explained by pro cycling coaches Chris Carmichael and Jim Rutberg:

“The HFLC [High Fat Low Carb] strategy has been shown to increase the utilization of fat for energy, especially in long-term (20 months) fat-adapted athletes (Volek, 2015). However, the oxygen cost of locomotion increases while exercising on a HFLC strategy (Burke, 2016). It takes approximately 20% more oxygen to liberate energy from fat compared to carbohydrate, which means relying primarily on fat reduces economy. This isn’t necessarily a problem, since you have a large supply of energy to burn, but these findings don’t indicate an IMPROVEMENT in endurance performance.”

Finally, it can take several months to become fat adapted, and during that time you will only make progress in becoming fat adapted and not in getting faster/stronger. You have to be able to weather that “pause” in your progress. I’m not an elite athlete by any means, but the idea that I’d have to experience several months of poor performance on the weight-lifting platform to become fat adapted is a hard pill to swallow. It’s a big commitment — both in time and in how strict you have to be in your diet, indefinitely, to stay in ketosis — with an unclear payoff.

Let’s do a quick review and summation of what we’ve discussed so far: If you want to get bigger, stronger, and faster, you’ve got to train long and hard; regardless of your fitness modality of choice, you’re sometimes going to perform bouts of intense exercise — anaerobic exercise. Anaerobic exercise requires glycogen to create ATP, which gives you the energy to push yourself. Glycogen comes from carbs.

So if you want to perform athletically at your best, you want to eat carbs, and lots of them.

The Other Big Advantage of a High-Carb Diet: Recovery 

Not only do carbohydrates improve your ability to perform athletically, they also improve what is arguably the even more important part of the training equation: recovery. It’s in recovery, not in the gym, when you actually get bigger, stronger, and faster. Carbs aid your recovery in two ways: increasing insulin production and increasing testosterone production.

Insulin Production. Many low-carb proponents argue that carbs make you fat because they spike insulin levels which directs glucose into fat cells. Yes, carbohydrates cause insulin to spike, but no, insulin itself does not cause fat cells to get bigger (that happens if you’ve got excess calories — composed of any kind of macronutrient — in your system).

But you know what insulin itself does cause to get bigger?

Muscle cells.

When insulin binds to receptors in your muscle cells, it signals to their ribosomes to start making more protein, which is then turned into muscle tissues. In the absence of insulin, this muscle building process doesn’t happen. So if you want bigger muscles, you need insulin.

Besides kicking off protein-muscle synthesis, insulin helps inhibit the breakdown of muscle tissue. Whenever you exercise, your body goes catabolic — that is, it starts breaking down nutrients and tissues to fuel itself, even muscle tissue. Insulin can help ensure you break down less muscle during these periods.

Finally, insulin is the hormone that shuttles certain amino acids into your cells so that the tears you create in your muscle tissues while lifting can be repaired, and so you can get bigger and stronger.

Insulin isn’t some boogeyman. Insulin is your muscle-building pal. And there’s nothing like carbohydrates to stimulate insulin release.

Testosterone Production. Besides providing the fuel your muscles need for long, hard workouts, carbohydrates also play an important role in testosterone production. Several studies have shown that when individuals go on a low-carb diet, testosterone levels go down, while cortisol levels go up. This is a hormonal recipe for muscle catabolism and decreased performance. This testosterone drop becomes especially pronounced when you’re engaging in high-intensity workouts. Conversely, when you eat a moderate-to-high carb diet, your testosterone stays at optimal levels.

If you feel absolutely bushed and drained for the whole day after your workout, and wake up surprisingly sore and fatigued, you’re probably not getting enough carbohydrates in your diet. Adding more carbs to your diet can be an absolute game-changer in your recovery, and get you feeling much less tired and much more energetic.

How to Eat a Low-Fat/High-Carb Diet

So you’re considering trying a high-carb/low-fat diet. What does that look like?

Well, very obviously, it’s a diet low in fat. It’s important to understand that we’re not reducing fat because fat is intrinsically bad. There’s absolutely nothing wrong with this macronutrient; it’s essential to a balanced and healthy diet, and remember your body uses all 3 metabolic pathways, and all 3 kinds of fuel, regardless of your main training modality. You need some fat for fuel too. Rather, we’re reducing fat because fat is calorically dense, so that it’s easy to eat too much of it, and reach your daily calorie goal, before you’ve consumed a sufficient amount of carbohydrates to maximize your athletic performance.

Now the definition of what constitutes “low” fat will vary by the person and what their goals are, but generally a diet is considered low-fat if you’re getting 20% or less of your calories from this macronutrient.

The rest of your daily calories will be divided amongst carbs and protein. The exact breakdown of these macronutrients will again vary depending on your goals; for example, if you’re trying to lose weight, your carb and protein percentages might be equal.

Here’s how to figure out your starting carbohydrate and fat consumption.

First, download MyFitnessPal so you can track your macronutrient consumption. If you buy the premium version, you can also set macro goals for yourself each day. Macro tracking keeps you honest. When you don’t track, you might think you’re eating high-carb/low-fat, when you’re really eating high-carb/high-fat; as we mentioned last time, a lot of foods you think of as “carby” actually contain a surprising amount of fat. You can easily end up eating a ton more calories from fat than you realize, which will prevent you from getting enough carbs without exceeding your overall calorie goal (which will result in weight gain).

Tracking is kind of a pain in the beginning, but after a few weeks it becomes second nature. You’ll even get to the point where you can eyeball portion sizes when you’re at a buffet or eating at home family style. Don’t worry about getting super accurate. Just make sure you’re in the ballpark.

Second, set your daily protein goal. When people either do high-fat or high-carb diets, they often give protein the short shrift. Protein is essential for building muscle and if you’re trying to lose weight, it does a great job of keeping you feeling full longer between meals. General recommendations for protein consumption range from .8g per pound of bodyweight to 1g per pound of bodyweight.

Your protein macro will rarely change. If you’re trying to lose or gain weight, you’ll want to tweak the carbs and protein first.

Third, determine your carbohydrate amount. This will depend on your fitness goals. If you’re trying to lose weight, aim to get 1g of carbohydrate per pound of bodyweight. If you’re trying to gain weight and get stronger, aim to get 2g of carbohydrates per pound of bodyweight. Make sure that those carbs you’re getting consist of at least 40g to 50g of fiber a day. This is to ensure you’re not just eating gummy bears to hit your carb goal. Plus fiber-rich whole foods have a lot of benefits for your hunger satiety, bowels, metabolism, and overall health.

Finally, determine fat amount. Again, this will depend on your fitness/diet goals. If you’re trying to lose weight, aim to get .27g of fat per pound of bodyweight. If you’re trying gain weight, aim for .5g of fat per pound of bodyweight.

Let’s bring this all together in an example. Steve is a 240-pound man who’s trying to lose weight. He plans on being active with weight lifting and hiking so wants to eat high-carb/low-fat so he has the energy to power through those workouts.

He sets his protein goal at 240g (240 lbs x1g), his carb goal at 240g (240 lbs x 1g), and his fat goal at 65g (240 lbs x .27g). That’s about 2,500 calories a day.

Percentage-wise, Steve will be getting about 38% of his calories from protein, 38% of his calories from carbs, and just 23% of his calories from fat. He’ll keep this macronutrient breakdown until he stops losing weight. Once he stops losing weight, he’ll need to reduce calories a bit more. He keeps protein and carbs the same, but reduces the fat by 100 calories. If he starts feeling overly fatigued during workouts, he may need to bump up calories. In that case, he’ll keep protein and fat the same, but bump up the carbs by 100 calories.

If you’re trying to gain muscle mass, your macro breakdown might be 50% of calories from carbs, 30% from protein, and 20% from fat. In fact, that’s what mine looks like right now.

There Is No One, True Diet

There’s a lot of chatter out there about what’s The One, True Diet.

And the answer is that there isn’t one.

My goal with this series wasn’t to prove that a high-carb/low-fat diet is superior to a low-carb/high-fat diet. It was to just push back against all the naysaying carbs have gotten in the past decade or so. Nutrition is complex. Genetics, environment, and physical activity all play a role in how your diet will affect you. You’ve got to know what your goals are and experiment. And you should consider all options, instead of leaning into whatever’s currently got the loudest hype.

If you’re pretty much sedentary, but you want to lose weight, then, yeah, a high-fat/low-carb diet will probably be your best bet in losing and keeping the weight off.  But I gotta ask, unless you have some sort of disability, why are you sedentary? Get moving! Physical activity plays a vital role in both your physical and mental health. Eating low-carb while sedentary can turn into a negative cycle, in which you have less energy and feel more poorly during exercise, which makes you want to exercise less, which makes you more sedentary.  

Personally, I really like the idea — both literally and symbolically — of taking in a lot of energy and burning up that energy, day in and day out. Wouldn’t you rather live a high-octane life, than to run on reserve battery-power that functions fine only because you remain tethered to a stationary dock?

Even if you’re just an amateur athlete, be an athlete! Perform your best. Push yourself. Be a beast. Keep the fire ever stoked, and ever burning. Live with thumos. 

If you’re super active and do intense activities like 5Ks, CrossFit, and weight lifting, then you could definitely stand to benefit from eating a good amount of carbs. They can help boost your performance considerably compared to a low-carb diet. You may think you’re performing decent on a lower-carb diet, but that’s because you’ve forgotten (or never truly known) how it feels on a high-carb diet. I’ve known folks who weren’t even trying to eat a low-carb diet, per se, but had just absorbed the contemporary anti-carb ethos, and consequently pared down their carbs here and there, who were amazed at how much better they felt once they intentionally lowered their fat and upped their carb intake. And for people who’ve been eating seriously low-carb for awhile, adding carbs back can result in an energy surge that feels downright magical.

But realize that choosing between high-carb and low-carb doesn’t have to be an either-or decision. If you like how you feel eating low-carb, and/or your genes predispose you to diabetes or other metabolic issues, then you should probably stick with it. It doesn’t mean you have to miss out completely on the performance benefits of carbohydrates though. You can try eating low-carb/high-fat most of the day and only consuming carbs before and after your workout when you’re most insulin sensitive and your muscles are more likely to slurp up that glucose into stored glycogen. Or you can take either the “Train Low, Train High” or “Train Low, Race High” approach. With the former, you do your slower, long-distance, endurance workouts coming off day(s) of low-carb eating, while you do your high intensity workouts coming off day(s) of higher-carb eating. With the latter, you do all your workouts on a low-carb diet, but fuel up on carbs before/during a race (keep in mind that being glycogen depleted during your training will prevent you from pushing yourself as hard, which stymies your progress in getting stronger/faster; you may find the trade-off worth it though).

Experiment and find what works for you. But as you formulate and test your hypotheses, keep an open mind and don’t rule out the inclusion of carbs in your protocol.

Michael Moran

Submitted by: Michael Moran in Lonsdale, MN, United States