Is low-carb necessary for fat loss?
You've heard all the claims.
Low-carbs is the BEST for fat loss!
If you're obese, you NEED to eat low-carb.
Insulin halts fat oxidation so eating things that spike insulin hinder fat loss.
I can't get lean unless I go on a low-carb diet.
Carbs are bad.
I am sure everyone has heard most of these statements. And the truly harmful ones are the blanket statements like "carbs are bad" because it shows an all-encompassing viewpoint based in ignorance, fear, confirmation bias and/or misunderstanding.
Perhaps the most frustrating thing is that people DO see success with low-carb diets which mean that in their mind, low-carb is the only approach. Sometimes people fall ass-backwards into a pretty good dietary approach, sometimes people succeed in spite of themselves, sometimes people just create a calorie deficit without even realizing it. So the thing is....low-carb (or even keto) can and do work but that doesn't mean they are the only thing that works.
Prompted by an excellent study that just came out, I figured it was time to dive into whether we need to be so worried about carbohydrates and fat loss. Should we be concerned with eating carbohydrates at each meal ultimately decreasing our insulin sensitivity? Should we be worried that spiking insulin will halt fat loss? And do most of us understand metabolism enough to make those calls?
Ultimately, no. Here's why:
Dispelling Low-Carb Dogma
A study released early this year called the DIETFITS study conducted and concluded the following:
“In this clinical trial of 609 generally healthy overweight or obese adults without diabetes who were randomly assigned to a healthy low-fat vs a healthy low-carbohydrate diet, there was no significant difference in weight loss at 12 months. In addition, there were no significant interactions between diet and 3 SNP multilocus genotype patterns or diet and baseline insulin secretion on 12-month weight loss...there were also no significant between-group differences observed for body mass index, body fat percentage, or waist circumference.”
“We conclude that when equal emphasis is given to high dietary quality for both low-fat and low carbohydrate eating plans, it is not helpful to preferentially direct an individual with high insulin secretion status who is seeking weight loss to follow a lower-carbohydrate eating plan instead of a lower-fat eating plan.”
We've got a few BIG things stacked up that this study knocks down.
1. As long as we're not talking about diabetics, even overweight/obese people can see fat loss on a higher carb diet. Yes, even with all that nasty 'ol insulin they were able to lean out. Perhaps the most overlooked aspect is that even higher insulin is not an issue for insulin sensitivity especially in a fat loss phase. Being in a calorie deficit will enhance insulin sensitivity and since the cells are not "over-fed" they handle the carbohydrate calories just fine. Being in a calorie surplus changes that scenario but that's now what we're discussing here.
2. They took into account the genotyping for insulin secretion. Yep, even high insulin secreters saw perfectly fine fat loss. I know you can send out for some blood/saliva work to determine what kind of macronutrient split you should follow but remember it's pretty irrelevant in a calorie deficit, as long as protein, fiber and whole foods are emphasized.
3. They took into account body mass, body fat percent and waist circumference. So this helps even out the potential wrinkles from seeing better "weight loss" on a low-carb diet. I don't know about you but I don't care about perceived fat loss from just losing some glycogen and water. Low-carbohydrate diets up the reward for many people because they see that huge initial weight drop....but it's smoke and mirrors.
My cat looks pretty big when he's got his winter coat. But when he gets a lion cut he looks half the size. The fur helps create the illusion of size just like a low-carb diet creates the illusion of faster progress because of water loss. But illusions are just that.
Confusion with insulin
Many people read the above or hear that "calories are more important than carbs" for fat loss but still can't let go of the insulin dogma.
Surely if someone is insulin resistant and they are also overweight, it makes sense that lowering overall insulin levels would help with weight loss. But it's the chicken or the egg scenario. In reality, chronic overeating will cause insulin resistance in cells. It is the constant abundance of nutrients and calories that make cells say "no more thank you" and develop resistance to insulin - they simply won't be as receptive to nutrients because the nutrients are in such abundance. Well.....who always says "yes please, more please".....fat cells.
When we look at this, we can see that insulin resistance is the product of chronically overeating. Overeating creates insulin resistance as a protective mechanism for cells and the excess calories go to fat. The fastest way to work on reversing this is to get your butt in a calorie deficit, the cells will gain sensitivity as you lose fat.
But the little truth you've heard about insulin halting fat loss is true. Good God man, if thats true then how could you eat carbohydrates and lose fat?! Doesn't this contradict what you just said above?
Nope, not in the least.
What you don't know your body is doing
Energy needs change on a daily basis, an hourly basis, a minute to minute basis. But homeostasis, or keeping your body in an even, normal state is priority #1. No matter what you read from Dr. Oz, your body is far more complex with an endless array or mechanisms in place to keep you alive and functioning.
Guess what happens if you don't eat for a few hours? Nothing. Heck if you didn't eat for three days you would still be alive. Hungry, but alive. Some small animals with lightning fast metabolisms perish much sooner. It's good not to be a mouse.
Any time you eat a meal you are probably ingesting more calories than you need at that exact moment. This is why your blood sugar is to tightly controlled.
-You have 5 liters of blood
-Fasting blood glucose in healthy people is 4ish gramsl (that's a freaking teaspoon of glucose by the way, a TEASPOON in 5 LITERS!!)
-Fasting blood glucose in diabetics is 6ish grams.
-Going from a fasting blood glucose of one to one and a half teaspoons is going from healthy to diabetes
That's how tightly regulated the system is. Which means when you eat a meal not all the amino acids, fatty acid and glucose get dumped into your bloodstream at once. It is titrated in. Insulin rises to help clear blood glucose and amino acids and this halts fat burning and enhances fat storage. But that is simply so your fat cells (and liver) have energu to release between meals when you aren't eating.
So its true that insulin halts fat loss. But times between meals and at night when you aren't eating and insulin is low, you're burning body fat. And those dips into using fat for fuel and lower insulin is MUCH greater when you are in a calorie deficit. Here's a simply graphic below to illustrate this:
If you're in a calorie deficit, the blue outweighs the green. If you're in a surplus the green outweighs the blue. Your insulin sensitivity is highly influenced by which color above is dominating.
Hence a calorie deficit being way more important than a low-carb diet.
Knocking back the carb haters
Someone is probably going to still throw a hissy fit over this. "But did you know that insulin suppresses HSL (hormone-sensitive lipase which breaks down fat into fatty acids to be burned)?". Yes, that is true. But guess what also suppresses HSL? Dietary fat. And if you want some proof of immediate insulin resistance look no further than a study conducted by Parry et all which showed that a single high-fat overfeeding caused impaired whole-body insulin sensitivity in healthy adults.
A fat storing hormone most people haven't hear of is acylation stimulating protein (ASP). ASP is stimulated by dietary fat. And ASP can cause a rise in insulin as well. So independent of carbohydrates you have hormones that store dietary fat as body fat and ALSO spike insulin.
Dietary fat is also the least thermogenic of all nutrients meaning it takes the least energy to metabolize. It has been shown to be the least satiating and is the most calorie dense. So it's not winning any awards in the thermogenic, fullness and calorie categories. #sorrynotsorry. But again, if calories are controlled this doesn't really matter.
Protein also causes a fast insulin spike. Whey protein is highly insulinogenic. Beef causes a steep insulin spike. Dairy causes a large insulin spike. So I guess you cant eat protein now either.
People love to overlook the fact the dietary fat is much more easily stored as body fat than carbohydrates or protein. It is much more metabolically efficient to store dietary fat as body fat. Of course, the rules apply here too; if you eat a high fat diet (even if dietary fat is easily stored as body fat) a calorie deficit renders this much less important.
Some people see a drastic rise in cortisol on a low-carb diet when they are exercising a lot and of course, restriciting calories. Cortisol is not the boogeyman but it does impair recovery and inhibit immune cells so a chronically elevated cortisol level can cause some burnout and energy disregulation. You might have trouble falling asleep or relaxing. You might feel on edge, burned out, tired and wired. Insulin suppresses cortisol and is anti-catabolic.
Insulin is also a satiety hormone. Say what?!
What this means for you
The study cited in the beginning helps to highlight how important it is to nail down a few basics. Eat optimal protein and fiber, focus on whole foods and create an appropriate calorie deficit. That gets you the results. Your personal preference is great if it keeps you adherent. But it doesn't mean because you WANT to follow a certain approach means it will work better. I've seen lots of clients try and fail numerous times on a dietary approach they PREFER to follow. So even preference isn't the end all be all.
More importantly, what dietary approach can you sustain? And are you eating enough protein, eating fruits and veggies? And of course, are you in a calorie deficit? That is the master switch in this process.
The reason a lot of fat loss diets end up being lower carb is because you won't decrease calorie from protein. And you can only go so low in dietary fat before you get some hormonal issues. So carbohydrates tend to be the variable calorie in a lot of people's approaches. But it doesn't mean carbs need to be at 15% while fat is at 50%. You can eat 25-30% fat and 40% carbs. That 40% at 1500 calories is less than 40% at 3000 calories but that's just because of the calorie difference. It's simple math.
Meet your basic fat needs but dont shy away from the carbohydrates. In addition to having no negative effects on fat loss you might just feel better training, enhance satiety, suppress cortisol, sleep better and feel more full from the increased food volume.
The science is there. Hopefully we can acknowledge it.