Chances are you’ve heard about many of the different types of low carb diets like the Atkins diet or the Ketogenic, Keto, diet. Maybe you've even tried a low carb diet and lost some “weight”, or you know someone who has, but is going low carb really an effective strategy for weight loss?
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First, let's make the important distinction between weight loss and fat loss. Your body is made up of two types of weight, fat mass and lean mass. Fat mass is your body fat and lean mass is made up of your muscle, bone, water, and organs. So, weight loss can occur by losing either fat mass or lean mass whereas fat loss refers to losing body fat only, which is exactly what you want.
You don’t want to lose muscle because muscle burns almost two times more calories per pound than fat making it easier to lose fat and allowing you to eat more without gaining fat. Of course, muscle also provides you with a strong physique that’s more resilient to injury. You don’t want to lose bone density for the same reason, as having a higher bone density makes you more resilient to bone injury. Then you don’t want to lose a lot of water either because of course that can lead to dehydration and when you rehydrate again you’ll simply gain the water weight back.
Losing significant amounts of water weight is exactly what happens in the initial stages of a low carb diet because carbohydrates are made up of mostly water, just as the second part of its name carbo-hydrate indicates, so when carbohydrate stores become depleted you’ll lose a significant amount of water weight. This is why you have to assess your body composition not just your weight so you can determine if the type of weight you’re losing from a low carb diet is lean mass or fat mass.
Next, let’s clarify exactly what a carbohydrate is. Carbohydrates are one of the three macronutrients, the other two are protein and fat, and are made up of different forms of sugar. There are two main categories of carbs, simple and complex.
Simple carbs are absorbed and digested faster than complex carbs because they’re already in their simple form. The three most common forms of sugar that we consume from food are glucose, fructose, and galactose. These three forms combine and create the three naturally occurring pairs of sugars found in food. The first is sucrose, which is table sugar, and is made up of half glucose and half fructose. The second is lactose, which is the sugar in dairy, and is made of up glucose and galactose. And the third is maltose, which is found in various grains like wheat and barley and is made up of two units of glucose.
Complex carbs are made up of three or more forms of sugar combined and are absorbed and digested slower than simple carbs because the larger combinations of sugars take more time to be digested. Complex carbs can be further categorized into two types. starchy carbs and fibrous, non-starchy, carbs. Starchy carbs contain higher amounts of glucose and lower amounts of fiber while fibrous, non-starchy, carbs contain mostly fiber, lower amounts of glucose, and high levels of vitamins and minerals. Examples of starchy carbs are potatoes, rice, grains, beans, and legumes whereas most vegetables are fibrous, non-starchy carbs.
Now, let's define what a low carb diet is. There’s no set definition but typically it’s defined as a diet that consists of less than 130 grams or less than 26 percent of daily calories per day from carbs. A very low carb diet like the keto diet consists of even less, typically less than 20 to 50 grams or less than 10 percent of daily calories per day from carbs. On the contrary, a high carb diet is typically defined as a diet that consists of 45 percent or more of calories per day from carbs.1
So, let’s go through how each of these carb intakes affects your metabolism and body composition starting with a high carb diet.
When you eat a high amount of carbs, glucose levels, otherwise known as blood sugar levels, rise significantly and an excess amount of glucose in the bloodstream is toxic to the brain, neurological, and cardiovascular systems so the hormone insulin is released from the pancreas to decrease blood sugar levels and drive the excess glucose into the muscle and liver cells as glycogen. Glycogen is the simply stored glucose in muscle and liver cells and its storage space is limited.
The average person can only store around 400 grams of glycogen, which is about 2,000 calories and glycogen stores are utilized mostly for high intensity exercise. So, if you’re on a high carb diet and you’re not doing much high intensity exercise then glycogen stores are already full and if you continue to consume a high intake of carbs then insulin levels become chronically elevated, and the excess glucose is converted into fat and driven into the fat cells. Obesity and Diabetes are developed when this happens chronically. Look at the Standard American diet, which is a high carb diet, and the high rates of obesity and diabetes in America. According to the most recent National Health and Nutrition Examination Survey published in February 2020, the age-adjusted prevalence of obesity in adults was 42.4 percent which is 2 in 5 people2 and According to The National Diabetes Statistics Report 37.3 million people, which is 11.3 percent of the US population, have diabetes.3
On a low carb diet glucose and insulin levels aren’t chronically elevated and glycogen stores aren’t full so there’s no excess of glucose to be stored as body fat. In this scenario, fat can be utilized more effectively as a fuel source.
On a very low carb diet like the ketogenic diet when glucose levels are even lower the body enters the state of ketosis which is when the liver manufactures ketones from fats to supply fuel to the brain, this process is called ketogenesis and it’s where the name of the diet is derived. The brain and nerves require about 20 calories per hour, waking or sleeping. On moderate or high carbohydrate diets glucose is the primary fuel source for the brain. This metabolic shift from utilizing glucose for fuel to utilizing fat for fuel also happens throughout the majority of the other cells in the body and causes stored fat to begin to be mobilized and burned for energy.
It’s often stated that glucose is the body’s “primary fuel”, but this is not true. It is true that all human cells can metabolize glucose for fuel, but the mitochondria, which are the energy producers in most cells, prefer to burn fat. So fat is the body’s preferred and primary fuel, except in specialist cells that lack mitochondria like red blood cells, or cells that lack ready access to fat like neurons, and when oxygen is limited as in muscle cells during high intensity exercise.4
So, the answer is yes, low carb diets are an effective strategy for weight loss, especially if you’re sedentary or only exercise at low to moderate intensities where fat is utilized as the primary fuel source.
If you’re regularly doing high intensity exercise like strength training and high intensity interval training where glucose is the primary fuel source then a moderate carb diet is going to be best for you because on a low carb diet the body won't have enough stored glycogen available which will decrease your performance and the body will manufacture glucose from protein, a process called gluconeogenesis, and since protein reserves are found in muscle and lean tissue this can lead to a loss of muscle mass. High intensity exercise can increase carb needs anywhere from 200 to 500 calories per hour of training.
Even though glucose is the primary fuel source used during high intensity exercise fat utilization is still high because of the total calories burned and the exercise post oxygen consumption or EPOC response which causes further increased caloric burn even in the hours after high intensity exercise. High intensity exercise of course will also help you increase your muscle mass, strength, and conditioning helping you reach your body composition goals faster and develop a strong physique.
Another major challenge with low carb diets is their sustainability, due to the restrictive nature of the diet they can be very difficult to stick to long term. So, based on your physical activity levels and lifestyle you can determine what level of carb intake is going to be most effective and sustainable for you. Then remember to regularly assess your body composition so you can objectively identify if what you’re doing is leading to a decrease in body fat and an increase or at least maintenance of muscle mass.
If you want to calculate not only how many carbs you should eat each day but also how much protein, fat, and total calories you should consume each day for fat loss make sure to read our previous article How to Calculate Calories and Macros To Lose Weight Fast.
Or if you’d rather have a coach to guide you step by step through the process of calculating your calories and macros and help you make the necessary adjustments along the way so you can sustainably achieve your body composition goals then click on PHP Coaching above to learn more.
Let me know in the comments below, have you ever tried a low carb diet and what was your experience like?
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References:
- Oh R, Gilani B, Uppaluri KR. Low Carbohydrate Diet. [Updated 2022 Jul 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537084/
- Hales CM, Carroll MD, Fryar CD, Ogden CL. Prevalence of Obesity and Severe Obesity Among Adults: United States, 2017-2018. NCHS Data Brief. 2020 Feb;(360):1-8. PMID: 32487284. https://pubmed.ncbi.nlm.nih.gov/32487284/
- Centers for Disease Control and Prevention. National Diabetes Statistics Report website. https://www.cdc.gov/diabetes/data/statistics-report/index.html. Accessed 2/14/23.
- Paul Jaminet Ph.D and Shou-Ching Jaminet Ph.D, Perfect Health Diet (Scribner, 2012), 102.
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