What is a Low Carb Diet and How Does It Work?

You’ve probably heard about them on the news, read about them on the internet, and some guy named Atkins keeps popping up on your search results. Low Carb diets aren’t terribly new, but they’ve blown up in popularity over the last couple years to the point where you can’t avoid talking about them anymore. Chances are, someone you know is on a Low Carb (Slow Carb, No Carb, GI Joe Carb…) diet right now!

So what the hell is it, really, and why should you care?

The Basics

Some quick definitions:

  • Carbohydrate: Commonly called “sugar” and “starch”, they contain 4 calories of energy per gram.
  • Fat: Also known as “dietary fats”, these are broken out into unsaturated (healthy), saturated (unhealthy), and trans (Danger, Will Robinson!) versions. They contain 9 calories of energy per gram.
  • Protein: Coming from animal sources and some plant sources, they contain 4 calories of energy per gram.

A Low Carb diet is exactly what it sounds like: you eat foods that contain little to no carbohydrates, meeting your energy needs by increasing dietary fat and protein intake per day. One of the most famous examples of this is The Atkins Diet, which had a big fad period back in the early 2000’s.  Since then, many other diets, fads, crazes, and methods have popped up doing essentially the same thing, but with slightly varied restrictions on what you can and cannot eat.

Lets Talk About Gluten For a Minute

I hear a lot of confusion out there about Gluten, and how it relates to wheat, bread, carbohydrates, low carb diets, Paleo, whatever. Lets take a minute to talk about what Gluten is, how it relates to Low Carb diets, and why it probably doesn’t matter for you.

That’s right, I’m going to talk about Gluten like it doesn’t matter for your diet! Yes, this puts me in a minority. No, I don’t care.

Gluten is not a carbohydrate. It’s a naturally occurring protein found in wheat and related grains like rye and barley. They make some breads chewy and help them rise when cooking. It’s added to a lot of products for different reasons, often as a food additive to add protein to foods that are naturally low protein, including imitation meats and some non-wheat bread products.

Gluten is not inherently bad for you, unless you have Celiac Disease, in which case you cannot process it correctly. Only about 1% of the U.S. population has Celiac Disease, so chances are you’re in the other 99%. There is a lot of detail we could talk about here, but suffice it to say that it has a strong genetic component and if you’re worried then ask your doctor to test you for it.

There is one other possible reason not to eat gluten, and that is Gluten Sensitivity. There are people who report sensitivity to gluten products, but who do not show full-blown Celiac Disease. However it should be noted that there are no decent studies showing that it is Gluten that causes the slight allergic reaction these people are experiencing. It is possible, and more likely, that Gluten Sensitivity is actually early stage Celiac Disease, or an allergic reaction to something else that is also contained in wheat products. An example substance is FODMAPs, which are carbs the body has a hard time digesting properly and can cause allergic-type reactions, much like Celiacs experience from Gluten, but with much lower severity and with a different ultimate cause.

Not all bread products contain Gluten, either. Only the wheat-based or gluten-fortified breads actually have it, so if you are experiencing sensitivity to all breads, don’t simply assume it’s Gluten causing the issue. Check the ingredients, and if Gluten isn’t there then it’s not the issue. You may have an allergy to something else in your bread!

You can have low carb diets with or without gluten, and you can have a gluten-free diet that is high in carbs. The thing to know and remember is that gluten is not dangerous by default, and it is not the same as carbohydrates.

Always make decisions from a position of knowledge.

How Does a Low Carb Diet Work?

Back to the Low Carb stuff!

Carbohydrates form a big part of the American diet, and they are incredibly easy to over eat. A single slice of whole wheat bread has about 15 grams of net carbohydrates (you can ignore Fiber, since you can’t digest it), which equates to 60 calories per slice. If you eat six slices of bread per day (toast in the morning, sandwich for lunch, garlic bread with dinner), you’re taking in 360 calories per day just from that bread. To put that into perspective, the average 170lb person needs about 1,700 calories to maintain their weight if they don’t exercise. Those few slices of bread would account for 21% of those calories, and that doesn’t include whatever you eat with it.

When you eat a moderate to high carb diet, you’re taking in 50% or more of your total daily calories from bread products. This poses a couple inherent problems based on how your feeling of hunger responds to carbohydrate:

1. You get a lot of calories from a smaller amount of food, which means you’re not eating as much as your body probably wants to eat in order to feel satiated. This prolongs your hunger response during meals, and may cause you to eat more than you intend or really need.

2. Carbohydrate-heavy foods tend to digest very quickly because the body is really good at breaking them down for fast usage. This means that after your meal is over (during which you may have already overeaten), you will become hungry sooner than you would have if you had eaten more fats/proteins and fewer carbs. Now, you’ll probably feel the urge to eat, even when you don’t need to.

Putting your hunger aside is hard enough, but we have to also take into account the fact that the body is great at putting carbohydrates where it thinks you need them. You really only have two options here: carbs sent to the muscles for energy production or carbs sent to be stored as fat. Here’s how that works in two different scenarios:

Good Scenario: You eat some carbohydrates, and then go running 10 minutes later. Your body decides that you need the energy from those digesting sugars Right Freakin’ Now, so it breaks them down and uses them to generate energy for the muscles right away. As long as it keeps finding dietary carbs to work with, you’ll keep fueling those pumping legs with those carbohydrates. Once you run out, your body starts using stored energy (fats, etc). This is a good time to be eating higher carbohydrates, because the stuff you eat isn’t being stored longer term to cause fat build up.

Bad Scenario: You eat some carbohydrates and then sit down to watch a Lost marathon on Netflix. Your body knows that you don’t need that energy right now, but it still has to do something with the stuff you ate. It digests the food and then puts it in long term storage (i.e. your fat cells) figuring it may need it in the future.

Your body is pretty keen on not starving to death, so if you don’t need energy now, it sure as hell isn’t letting it go! When this happens, you’ve gotten just a little bit fatter than you were before. Will you notice? Probably not today, tomorrow, or even next week, but if this is a regular habit then you will be seeing some new love handles sooner rather than later! So what do you do?

Since most people don’t want to burn an extra 600+ calories per day via exercise (especially when you already exercise) to take care of their carbohydrate excess, your other option is to reduce the carbohydrates intake itself. This attacks the root of the problem, rather then trying to trim the branches because the body doesn’t process dietary fats and proteins the same way it processes carbohydrates. The fat and protein you take in provide a longer period of satiation because of these digestive differences, and they “sit heavier” in the stomach for longer periods of time.

Some studies have even shown that the brain reacts differently to simple carbohydrates (which are the most common in processed foods), causing a drug-like addictive response. Researchers from the New Balance Foundation Obesity Prevention Center at Boston Children’s Hospital reported in The American Journal of Clinical Nutrition (June 26th, 2013 issue) that they saw this in obese patients when they did fMRI scans of their brains while drinking two different milkshakes. When the participants were given milkshakes that were identical in sweetness, flavor, and calorie content but differing only in the number of simple carbs present, they found that the milkshakes with more simple carbs elicited a strong response in the addiction center of the brain (the nucleus accumbens). The other shake didn’t.

Whether or not the milkshake with more simple carbohydrates was able to bring more boys to the yard, however, is unclear at this time.

So, your brain thinks that sugars are basically cocaine, and we all know cocaine is not the best thing for you. So maybe cut down a little?

How Do You Follow a Low Carb Diet?

In a low carb diet, you typically do two things: determine how many calories you need to eat per day, and reallocate your calories so that more come from proteins/fats then carbohydrates.

Step 1: How much should you eat?

There are a lot of ways to find your Basal Metabolic Rate, or BMR. Body Composition assessments are one of the best way to do so, because they take your body fat and muscle into account. You can get a decent estimate by using a basic calculator though, which accounts for age, gender, height, and weight.

Like this one!

[calc id=744]

If you like to do some math yourself (or the calculator doesn’t show up), you can also use one of the following formulas to find your BMR:

Imperial (pounds, inches) Formula:

Women: BMR = 655 + ( 4.35 x weight in pounds ) + ( 4.7 x height in inches ) – ( 4.7 x age in years )

Men: BMR = 66 + ( 6.23 x weight in pounds ) + ( 12.7 x height in inches ) – ( 6.8 x age in year )

Metric (kilograms, centimeters) BMR Formula:

Women: BMR = 655 + ( 9.6 x weight in kilos ) + ( 1.8 x height in cm ) – ( 4.7 x age in years )

Men: BMR = 66 + ( 13.7 x weight in kilos ) + ( 5 x height in cm ) – ( 6.8 x age in years )

Conversions (if you have mixed units):

1 pound= 0.453592 kilogram

1 kilogram= 2.204624420183777 pound

1 inch = 2.54 centimeters

1 centimeter = 0.393701 inches

And finally, if you really need to do it quick and dirty, but don’t have any calculator stuff handy, you can do a rough estimation with this method:

BMR = Body Weight (pounds) x 10.5

These will give you the estimated number of calories you should be consuming in order to maintain your current weight and body composition. If you do anything other than just living in a day (which is most of us), then you need to factor in activity and exercise as well. We can do that pretty easily:

Sedentary (no exercise daily, desk job): BMR x 1.10

Lightly Active (exercise 15 min per day): BMR x 1.20

Moderately Active (exercise 30 min per day): BMR x 1.30

Highly Active (exercise 60+ min per day): BMR x 1.40

BAM! Now you know how many calories you need.

Step 2: Where should your calories come from?

With low carb diets you are focusing most of your eating on proteins and healthy fats. To figure out how much of these you should eat in a day, you can use these simple guidelines:

1. Eat no more than 50 grams of carbohydrates per day

2. Eat 1 to 1.2 grams of protein per pound of body weight each day

3. Eat enough healthy (unsaturated) fats to make up the rest of the calories you need

4. Eat whole, healthy foods with minimal processing. Give preference to naturally occurring foods and not crap in boxes. If you can eat it right out of the ground/off the tree/from the animal with nothing more than some cooking and seasoning, you’re probably good to go!

If you’re interested in seeing how the calculations play out, read on to the next section.

If not, I’ll bid you a fond adieu and see you next time!

Calculation Examples (Warning: Math Content!)

Lets take an example and break it down from start to finish:


30 years old
5’9″ tall

BMR Calculations:

From calculator above: 1,794.72 calories/day

From Imperial Men’s Formula: 66 + ( 6.23 x 170 ) + ( 12.7 x 69 ) – ( 6.8 x 30 ) = 66 + 1059.1 + 876.3 – 204 = 1797.4 calories/day

From Quick & Dirty Formula: 170 x 10.5 = 1,785 calories/day

Average: ( 1,794.72 + 1797.4 + 1785 ) / 3 = 1,792.4 calories/day

Activity Level:

Highly Active: 1,792.4 x 1.40 = 2509.36 calories/day

Macronutrient Calculations:

Carbs: 50 grams = 200 calories/day

Protein: 170 x 1.2 g/day = 204 g/day = 816 calories/day

Fat: 2509.36 – 200 – 816 = 1,493.36 calories/day = 165.93 grams/day