Extremely Low Carb Diets: The Science

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Defining “Carbohydrate” – Some Science Speak

Before we begin, let’s first define what a carbohydrate is (and isn’t).

Carbohydrate literally means “hydrated carbon.” In super science terms, when something is “hydrated,” it contains hydrogen and oxygen (H2O). The chemical abbreviation for a carbohydrate is CHO, so it contains a carbon, hydrogen, and oxygen molecule (Thompson et al. 113).

In simpler terms: It’s an energy source for the entire body. Energy is what makes the body function. Everything your body does on a daily basis from digestion to breathing to making your heart beat requires energy. Our bodies prefer to get this energy from carbohydrates.

Most of the time, these carbs are found in plant foods, such as fruits, vegetables, and grains (rice, cereal, bread, etc.).

Carbs are classified in 2 different ways: simple or complex, and they are classified as such based off of how many sugar molecules they contain. I won’t bore you with all of the details of that. The takeaway is that simple carbs are processed more quickly in the body because they are less complex. Complex carbs are processed more slowly because the body has to do more work to digest them.

Usually, when people are placing carbs in a negative light, it’s based off of simple carbs because simple carbs are our “sugars.” Sugars are not a bad thing, but they do have some considerations.

Here is a list of simple carbs. Do any of them sound familiar?

  • Glucose
  • Fructose
  • Galactose
  • Ribose
  • Lactose
  • Maltose
  • Sucrose

Glucose, fructose, lactose, and sucrose are likely the terms you have heard the most often. Let’s look quickly at what these are as a refresher:

  • Glucose: this is our body’s energy source. You may have heard a lot about glucose in relation to diabetes and insulin resistance. Glucose is extremely abundance in our diets and our bodies because this is what our bodies primarily use to carry out its daily functions.
  • Fructose: sweetest natural sugar found in fruits and vegetables. Sometimes called levulose or fruit sugar. It is a component in high fructose corn syrup.
  • Lactose: aka milk sugar. Found in all milk including human breast milk. Lactose intolerance means you do not make enough of the enzyme lactase to break down lactose, causing digestive upset.
  • Sucrose: contains fructose and is the sweet taste in honey, maple syrup, fruits, and vegetables. Table sugar, brown sugar, powdered sugar, and many others are made by refining the sucrose found in sugarcane and sugar beets.

I will likely discuss sugars and sweeteners at a later time. For now, keep these in mind because they become important when discussing low carb diets.

Here are some complex carbs you may have heard of:

  • Glycogen: our bodies store glucose in the muscles and liver. When glucose is stored, it is stored as this molecule.
  • Starch: Plants’ stored version of glucose. Grains (wheat, rice, corn, etc), legumes (peas, beans, lentils), and tubers (potatoes and yams) are high in starch.
  • Fiber: this is a complex topic, but you likely have heard of fiber for its benefits to help with digestion. It is found in many fruits and vegetables. It’s classified by “soluble” vs “insoluble.” Soluble means it will dissolve in water, whereas insoluble will not. Insoluble fiber is the fiber that’s recommended to help add “bulk” to help regulate bowel movements.

That was a long-winded but also overly-simplified explanation of carbs. Let’s look at why our bodies NEED carbs next.

It’s important to know too that all carbs, regardless of their starting structure, end up as glucose (sugar).

Carbs Provide Energy for Daily Activities & Exercise

Because most of my nutrition training began in sports nutrition, I am hyperaware of the importance of carbohydrates for any athletic endeavors. However, carbs are extremely important for everyone.

Here are a few quick bullet points as to what carbs do for our bodies:

  • Our bodies PREFER to use carbs for energy (we’ll discuss in a moment what’s going on when our bodies begin using fat and/or protein instead).
  • Our red blood cells can ONLY use glucose; brain/nerve tissues rely primarily on glucose. This is why you may feel tired, irritable, and shaky when you have not eaten carbs for a prolonged period of time.
  • Glucose can be broken down very quickly in times when our bodies need energy fast, such as during exercise.
  • Carbs spare protein and prevent ketoacidosis (discussed in a moment).
  • Fiber is important to help us stay healthy as they promote bowel regularity, and it can play a role in a reducing risk of colon cancer and cardiovascular disease.

What happens when we eat very few carbs (< 100g) on a daily basis?

When carbs (and thus glucose) is scarce, the body will make its own glucose from protein. This involves breaking down proteins in blood and tissues into the “building blocks” of protein called amino acids. These amino acids will then be converted into glucose. The fancy term for this process is gluconeogenesis.

If our body has a way to make glucose, then a low carb diet can be good, right? Well, it’s not without its issues.

There are 21 total amino acids, 9 of which we must get from our diet. Each of these amino acids has a specific function in our body. If amino acids are being pulled to create glucose, then they cannot be used for their other critical functions. Amino acids have roles in new cell generation, repairing damaged tissues, and supporting our immune system.

During starvation or extremely low-carb diets, our body will pull amino acids from our blood first, and then begin pulling from other tissues (such as our heart, liver, and kidneys). Over a prolonged period of time, this can cause potentially irreversible damage to these organs.

For those who are athletic, this means that your muscles will begin to get broken down, and it will be very difficult to maintain or build muscle mass.

But our bodies can use fat as fuel, right?

Technically yes, but it’s not ideal.

This is where we will talk about ketones and ketosis, popular buzzwords in the fad diet “Ketogenic.”

Our bodies already use fat as “fuel.” It’s the main energy source when our body is at rest and during lower intensity activities (e.g., sitting, standing, walking at a leisurely pace). Even at rest, though, our bodies will STILL use glucose for brain cells and red blood cells.

When carb intake is very low, the body will seek an alternative fuel source. Enter: fat. It will begin to break down fat as its fuel source through a process called ketosis. The result of ketosis is ketones.

Ketosis is important, and it is something our bodies already do. It provides energy to our brains during sleep, vigorous exercise, and other situations that will acutely deplete glycogen stores. Prolonged inadequate carb intake will cause the body to produce excessive ketones, which can be risky.

Ketones are acids, and high ketone levels cause the blood to become acidic. This condition is called ketoacidosis, which interferes with bodily functions, causes loss in lean body mass, and damages tissues. Ketoacidosis is seen most often with those who have untreated or poorly managed diabetes; this can be life threatening.

How a Ketogenic Diet Works

The idea behind Keto is that you deprive your body of carbohydrates (less than 50g per day). When this happens, your body will run out of glucose in the blood and then have to turn to alternative fuel sources – protein and fat. It usually takes 3-4 days for this to occur and to enter “ketosis.” This WILL make you lose weight; however, it is mostly from muscle breakdown, water loss, and calorie deficits. Keto can be used for rapid weight loss in the short term, but it is rarely recommended as a long-term diet solution.

The keto diet started in the 1920s-30s as a treatment for epilepsy, instead of fasting regimens that had been used since as early as 500 B.C. With the development of anticonvulsant medications, this is rarely used anymore.

A common misconception is that its intended use is for diabetes, specifically Type II diabetes. The science surrounding this is complicated, but it’s not that simple. If you have diabetes or any level of insulin resistance, it’s important that you work with a registered dietician as soon as you can and not try to “fix” it on your own through nutrition. Even medical doctors are misguided when it comes to this stuff due to their lack of proper nutrition training; this is why RDs exist and why we should utilize them as much as possible. There are some thoughts that this diet could also be used today to treat a number of specific conditions, though the research is not in agreement on any of that yet.

At the end of the day, people who are using the keto diet just for weight loss should be aware that there are more effective methods, and this form of long-term extreme restriction can be both physically and mentally harmful.

Ok – we get it. We have to eat carbs. How many a day?

The recommended daily allowance (RDA) for adults is based off of how much glucose is estimated to be used by the brain daily.

RDA for adults 19 years and older = 130g per day. This amount is usually too low for most people as this amount is ONLY what’s needed by the brain, and not what’s needed to support daily activities and exercise. It is the bare minimum to ensure adequate supply of glucose reaches the brain.

The optimal amount for someone will vary, and it widely comes down to what your daily life activities are, especially how much intentional exercise you engage in. The amount could be around 200g, or it could be as high as 500g. In short: it depends. Active people generally speaking should consider 3g/kg/day for light activity (up to 1 hr of exercise), and as much as 10g/kg/day if extremely active (4+ hrs training per day).

But sugars are still bad, right?

No. Sugar is sugar is sugar. When it comes to simple carbohydrates, the body does not entirely distinguish between if it’s sugar from an apple or sugar from a piece of candy; it all ends up exactly the same way. There are some thoughts surrounding glycemic index or glycemic load, but I’m not going to touch that in this post as it’s complex and very controversial, even among the nutrition professional community.

While focusing on getting complex carbohydrates has many health benefits beyond just caloric intake or potential insulin spike, at the end of day, sugars do not inherently “make you fat.” But even if they did, that’s not necessarily a problem either (a rant for another day….). Even complex carbs, though, end up as glucose in the body, as discussed earlier.

Energy balance (calories in vs calories out) is what the biggest influence is on weight for those that have normal functioning metabolisms (which many don’t such as myself; this is important to remember, too).

At the end of the day, extremely low-carb diets are not ideal, even for the purposes of short-term weight loss. Healthcare provider recommendations and supervision of course override anything here as YOUR specific needs may not match the general science and recommendations.

If you have further questions, feel free to contact me. I provide a number of services, and I am also working on a full crash course in nutrition, where you will learn about carbohydrates in a little bit more depth (anticipated launch of this course is September 2022).

Disclaimer: I am a nutrition professional (Sports Nutrition Coach, Advanced Sports Nutrition CE from Human Kinetics, and Precision Nutrition L1 Coach, and avid science enthusiast and hobbyist – still, NOT a dietician) but not YOUR nutrition professional. Please always follow your own providers’ recommendations. The information presented in this post is for educational purposes only and is not intended as a recommendation for you.

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