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Q & A: Carbs and Weight Loss

Fat and carbs

Paleo cuts out the major carbohydrate sources in the typical American diet, so it’s easy to assume that it’s designed to be a low-carb diet. But in fact, that’s not true: non-toxic carbohydrate sources (like potatoes and sweet potatoes) are perfectly healthy from a Paleo perspective.

But what about weight loss? Do you need to cut carbs to lose weight? Many people still believe that carbs are OK if you’re lean and active, but you should avoid them for weight loss. This isn’t quite as cut-and-dry as it appears, though. Take a look at some common questions, comments, and concerns about carbs, and whether or not they actually hold water (click on the links below to go to each question, or read straight through to see them all):

Do carbs cause weight gain?
Do you need to cut carbs for weight loss?
Don’t carbs send you on a blood sugar rollercoaster?
Don’t carbs spike your insulin and cause you to gain fat?
Does it matter whether or not you eat carbs with fat?
Does carbohydrate timing (morning vs. evening) matter?
What was carb intake like in the Paleolithic?

Do Carbs Cause Weight Gain?

The short answer: no.

Carbs do not cause weight gain. An inability to metabolize carbs causes weight gain.

In your body, carbohydrates have three potential uses: they can be used for energy immediately, sent to your muscles and stored as glycogen (energy for later), or sent to your adipose tissue and stored as fat. The hormone in charge of this is insulin. Insulin is released in response to high blood sugar, because high blood sugar is actually quite dangerous; insulin’s job is basically to get glucose out of your blood and put it somewhere more useful.

The first destination choice for that glucose is the brain (where it’s used as energy) or the muscle tissue and the liver (where it’s is stored as glycogen to be used as exercise fuel). But these organs only need so much glucose. So even in healthy people, insulin also functions as a “fat storage” hormone, sending the rest of the carbs to your fat cells.

But this doesn’t mean that insulin makes you fat. You don’t want to walk around with a nutrient drip in your arm all the time, so you need some way of saving food for times in between meals, and that’s what fat does: it stores energy for later! In healthy people who are eating an appropriate diet, insulin levels drop after the glucose is out of your bloodstream, and the body can dip right back into those fat stores in between meals.

So far, so good. But now think about what happens if there is no “time between meals” because you’re constantly grazing on carbs all day long. Tack on a sedentary lifestyle (very little glucose required for muscle fuel), and it’s a recipe for disaster. Insulin stays high, storing fat for a “fast” that never arrives.

The combination of carbs and inactivity creates a state called insulin resistance. Your body keeps producing more and more insulin, trying to cram the carbohydrates into your muscles and organs, but there’s just no room, and eventually the muscles stop listening to the insulin signal. So the carbs get shoved into fat stores as a last resort – but because you’re constantly eating more carbs, insulin levels never drop, and those fat stores never get used: they just stay put, storing up energy for a famine that’s never going to come.

What can we learn from this? Metabolically healthy people have nothing to fear from carbs, in amounts appropriate for their activity level. For people with metabolic disorders (like insulin resistance or metabolic syndrome), the focus should be on healing the metabolism, not avoiding carbs forever. Low-carbing (or even ketosis) can be a very useful Band-aid or a way of restoring metabolic health, but the ultimate goal should be a healthy metabolism capable of handling all kinds of fuel sources.

Do I Need to cut Carbs for Weight Loss?

The short answer: it depends. If you’re coming off a diet of Chex Mix and Cheerios, you may need to cut carbs relative to what you’ve been eating. But lower is not always better. The key is to find the “sweet spot” of carb intake that your body feels comfortable with, neither too high nor too low. And believe it or not, there is such a thing as “too low.”

That’s because your thyroid – the organ that controls your entire metabolism – needs carbohydrates to make the hormones that keep your body running. Inadequate carb intake is a signal of nutrient scarcity: your thyroid assumes there is a famine, and reacts accordingly.

If your body thinks there is a famine going on, it will hold on to every scrap of fat it can get.

Sweet potato

Your thyroid does not understand your weight-loss goals. It only understands the need to keep you alive. And since we all evolved in a world where food was scarce and precious, the thyroid is very trigger-happy about potential famines. Not enough food coming in? Batten down the hatches, slow the metabolic rate, decrease body temperature, shut off reproductive and immune function: anything to spare the energy necessary to let you get up and hunt some more food.

This is the last thing you want if you’re trying to lose weight.

So how can you avoid the scarcity-fueled thyroid panic? Simple: eat enough food, and eat enough carbs. Glucose (the carbohydrate found in starchy foods like potatoes) sends a hormonal signal that everything is humming along just fine, there’s no famine, and it’s safe to let go of any extra body fat because your next meal is assured.

That’s why you don’t necessarily want to cut out all carbohydrates to lose weight. Ketosis can work for some people, but not everyone responds well to it, and it’s not necessary.

What About my Blood Sugar?

You’ve probably heard a version of the “carbs spike your blood sugar” story as part of the justification to go Paleo in the first place. This is the familiar “rollercoaster” of blood sugar highs and crashes, accompanied by constant, insistent hunger and wild energy swings. It’s true that this does happen – in people who are metabolically sick.

But you just can’t generalize from people who are metabolically sick to everyone else. Take a look at what the hard scientific evidence actually says about carbs, blood sugar, and hunger:

The short story: the right carbs won’t send your blood sugar spiking and crashing – or if they do, it’s time to see a doctor, not fiddle with your diet. A low-carb diet may be a good “reset” for the first few weeks of weight loss, but it’s not necessary to continue once your metabolism has recovered enough to handle carbohydrates again.

Carbs, Insulin, and Fat Storage

But carbs spike your insulin levels, and insulin is a fat storage hormone, right? So how does it make sense to eat carbs when you’re trying to lose fat?

Take a look at the section on “Do carbs cause weight gain?” above. In diabetics, it really does work like this. But for the 95.7% of US adults who aren’t diabetic, it’s not the same:

The upshot: the insulin response from eating a healthy amount of unrefined carbohydrates in the form of whole foods does not “make you fat.” Again, if you have metabolic syndrome or insulin resistance issues, a temporary low-carb diet may be helpful, but continuing it in the long term is not useful.

But I Gain Weight Immediately When I Eat Carbs!

Do you eat a potato and then magically gain 5 pounds overnight? And then promptly panic and start restricting everything from beets to eggplant as “too carby?”

That can happen if you’ve been on a low-carb diet for a while and then re-introduce carbs. But here’s the thing: there’s an adjustment period for carbs just like there’s an adjustment period for low-carb. If you’ve ever tried a ketogenic diet you probably remember the “low-carb flu,” that week or two of feeling like a zombie on sedatives as you struggled to get off the blood sugar rollercoaster and switch to a fat-burning metabolism. Adding some more starch to your diet also has an adjustment period.

The reason why low-carb dieters see a temporary weight gain when they add in carbs is simple: glycogen and water weight.

  1. Glycogen: glycogen is the storage form of glucose, used for packing the glucose away in your muscles until it’s needed. After a carb re-feed, most adults will store about 1 pound of glycogen in their muscles. This is not fat. It’s fuel, waiting to be used. Your car does not “get fat” when you put gas in it, and you did not “get fat” because you gave your muscles some fuel.
  2. Water weight: the stored glycogen also soaks up a lot of water – to be specific, 4 grams of water to each gram of glycogen. This is not fat either. It’s just water. Think of it this way: if you drink 2 cups (16 ounces) of water and then step on the scale immediately without going to the bathroom, you will have “gained 1 pound” from the water in your stomach. Does that mean the water made you fat? No! Retaining water from stored glycogen is no different.

Together, the water weight and glycogen can cause the needle on the scale to go up 5 pounds, even though you haven’t gained any fat at all. This is normal and healthy, and nothing to worry about: stick with it for at least two or three weeks before you draw any conclusions about carbs “making you gain weight.”

Can/Should you Eat Carbs with Fat?

Coconut oilThere are two schools of thought on this:

The first one is just not true. Take a look at this study. The researchers gave two groups of obese patients a diet with roughly the same macronutrient ratios, but one group separated their macronutrients (eating carbs and fat separately) while the other group just ate normally. Both diets resulted in the same weight loss – in fact, the “carbs and fat together” group actually lost a little bit more. Both groups were otherwise the same in every way, including their insulin and blood sugar levels.

This study does a great job of describing how this myth got started – researchers took a high-carb breakfast and added more calories to it in the form of additional fat. Obviously, this resulted in more fat being stored, since more calories were added to the meal. But if you keep calories constant and simply adjust the proportions of fat and carbs, there’s no difference: fat does not get stored as fat just because carbs are there.

What about the other side of the question: should you actually make an effort to eat your carbs and fat together? The reasoning behind this is that fat makes your stomach empty more slowly, which helps reduce the glycemic response (blood sugar and insulin spike) after a meal.

The evidence for this is very mixed, with some studies finding good results and others finding not much difference at all. In fact, protein, not fat, actually seems to be better at blunting the glycemic response to a meal: this study (replacing carbs with protein or fat) and this one (adding protein or fat to a given amount of carbs) both found that protein was more effective. But it certainly is tasty to eat fat with carbs, and it’s possible that there’s a benefit, at least for some people, so if you like butter on your potatoes go ahead and add it!

Does Carbohydrate Timing Matter?

Yes, and no. Take a look at the specific times that you might have read about eating (or not eating) carbs:

Eat carbs in the morning/don’t eat carbs after 6pm.

The argument for this one usually has something to do with insulin sensitivity being higher in the morning. But in fact, many diabetics notice exactly the opposite (morning insulin resistance, called the “dawn phenomenon”), and this study found that subjects actually lost more weight when they ate the majority of their carbohydrates at dinner. So there’s no scientific evidence to support the idea that carbohydrates will magically make you gain weight if you eat them after a certain time of day.

Eat carbs in the evening to help you sleep.

So if the subjects in the study above lost more weight when they ate their carbs towards the end of the day, should you copy them and only eat starch during the evening hours?

If you like it that way, there’s nothing wrong with that. For some people, it may help reduce energy swings and hunger during the day, since fat provides more of a “slow and steady” fuel. And eating carbs in the evening may also increase the levels of a neurotransmitter called serotonin, which is responsible for feelings of contentment and relaxation – hence the idea that carbohydrates will help you sleep at night. But there’s also no reason to avoid carbs in the morning if you like them with your breakfast, especially if you work out during the early part of the day (see below).

Only eat carbs after a workout.

There is some truth to this one: after a workout, your muscles are hungry for fuel in the form of glycogen (carbs), and your body is well prepared to store the carbs as energy instead of fat. Most people who do reasonably intense workouts will feel and perform better with some carbs in their diet, and carbs immediately after a workout may be helpful for recovery and muscle gain.

On the other hand, the research into this is actually a lot less definitive than you might think, and it’s more important to get enough carbs over the course of the whole day, rather than worrying about squeezing them into the post-workout window. The idea that you should only eat carbs right after a workout is just unnecessarily restrictive: exercise increases insulin sensitivity for up to 48 hours after you hit the gym, so there’s no magical 30-minute window to cram in your carbs for the day.

Carb Intake in the Paleolithic

This is almost a nonissue because it shouldn’t really matter what cavemen ate: what matters is how human beings today can be healthiest, and to learn that, we don’t need a lot of speculation about prehistoric cuisine. But it deserves a brief mention because there’s so much misinformation out there. As far as we know, the “Paleo diet” was not necessarily low-carb.

Hunter-gatherer diets (our best modern-day estimation for Paleolithic diets) are not uniformly low-carb – or uniformly anything else. People living towards the equator tend to eat more carbs; people living towards the poles tend to eat fewer carbs. People who claim that they’re all low-carb tend to fixate on the Inuit or a few other groups, and ignore the big picture. Hunter-gatherer groups get their carbs from tubers, fruit starchy nuts, and other plant foods; there’s no reason to suspect that these foods were not available in some form back in the pre-agricultural era.

Getting much more detailed than that is really an exercise in guesswork: prehistoric potatoes rotted away without leaving us any fossil records, and we’ll probably never know for sure what a typical caveman actually ate. But all the evidence we do have points to a very varied range of “Paleo diets:” some higher in carbs, some lower in carbs, and others almost zero-carb. Humans are just adaptable like that; it’s one of our biggest evolutionary advantages. There’s no justification for saying that we’re evolutionarily maladapted to carbohydrates in general, and no need to be afraid of carbs based on some wild speculation about cavemen chasing mammoths.


Hopefully, this article should help put to rest some of the persistent myths about carbohydrates and weight loss that can trap you in an unnecessarily restrictive diet or even hamper your athletic performance. While a low-carb diet may be helpful for restoring insulin sensitivity at the very beginning of your weight loss efforts, eliminating carbs is not required for weight loss in the long term – and there’s very little actual evidence supporting the idea that scheduling your carbs down to the minute will do anything but waste your time.

People with metabolic disorders, like diabetes or insulin resistance, may benefit from a period of low-carb dieting to help their body recover, but the fact that something is an effective intervention for sick people does not make it required (or even better) for healthy people. Carbohydrates are important – for fertility, for immune function, for thyroid health, for athletic performance, and for mental health. And none of that changes if you’re trying to lose weight. So don’t be afraid of carbs: eat them, enjoy them, and enjoy the positive health benefits they can bring you.

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Hi I’m Ashley, I’m an ADAPT Certified Functional Health Coach

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