How Many Grams of Carbs Per Day Do We Need to Function?

Table of Contents
1. Why Do We Need Carbs to Function?
2. How Many Grams of Carbs Per Day Does the Average Adult Need?
3. Can We Live Healthy Lives Without Eating Carbs?
4. The Dangers of Eating Too Few Carbs
5. How to Calculate Your Carbohydrate Requirements

The relationship most people have with carbs is complicated. There are a lot of different opinions out there on how many grams of carbs we should be consuming on a daily basis.

Carbohydrates are one of the most important macronutrients we can consume as human beings. Carbs provide us with the energy we need to thrive.

However, carbs can also be problematic. Some types of carbs such as certain simple carbs like white pasta noodles are often responsible for weight gain. Eating these ‘bad’ carbs can result in a range of other issues associated with them, such as sugar spikes and crashes leading to lethargy. Even the more nutrient-dense complex carbohydrates are often avoided by people following low-carb diets designed for rapid and sustainable weight loss.

To make matters worse, the information we have about carbohydrates as consumers can be difficult to understand. While most experts agree we need some carbohydrates in our diets to function, guidelines around exactly how much you need to eat are murky.

The Keto diet, for example, suggests limiting your carb consumption to just 40g of carbs per  day, while the USDA indicates that approximately 45-65% of our daily carbohydrate intake should come from carbohydrates.

So, where does the truth lie? How many grams of carbs per day do we really need to function optimally?

Why Do We Need Carbs to Function?

While guidelines around carb intake can vary, most experts do agree that carbohydrates are a central part of a healthy diet. Carbohydrates are one of the three macronutrients found in our daily meals, alongside fats and protein.

The carbs we eat are broken down into sugars, such as glucose, fructose, and galactose. These sugars fuel the muscles, central nervous system, and other critical areas of the body. According to studies, the mammalian brain (including the human brain) utilizes glucose as its primary source of energy. We need at least some glucose in our diet to support brain physiology.

Since our body can’t function without our brain, it’s safe to say carbohydrates are necessary.

The glucose created when carbohydrates are digested is also stored in the muscles as “glycogen”, which ensures we have the energy we need to remain active.

Fiber, the part of the carbohydrate in a complex carb not broken down by the body during digestion, also has a variety of functions. Fiber in our diet helps with weight management and feelings of satiety. At the same time, insoluble fiber helps to promote healthy digestion, while soluble fiber reduces cholesterol, and assists with blood glucose regulation.

How Many Grams of Carbs Per Day Does the Average Adult Need?

The daily recommended intake of carbs  among men and women is approximately 45-65% of your caloric intake. If you eat a 2,000 calorie diet, for example, this means you’d aim to consume approximately 225 to 325 grams of carbs per day.

While this is the recommended number of carbs for most people, there are circumstances where you might want to reduce your intake of carbs. People with diabetes often need to reduce their carbohydrate intake to control blood sugar levels, for instance. Similarly, those on the Keto diet or a similar low-calorie food plan will also reduce their carb consumption.

According to the National Academy of Medicine, how many grams of carbs per day needed to keep your brain functioning properly is much lower than the recommended daily value. These researchers say that adults need around 130 grams of carbs today to produce enough glucose for the brain to function, and red blood cells to behave normally.

So, how can people survive on the Keto diet?

The Keto diet suggests how many grams of carbs per day needed is not much at all, and that 40g per day is enough. There are some people who believe we don’t need to eat carbs at all, provided we’re getting the right alternative macronutrients and micronutrients.

This is because carbs are not the only substance capable of producing glucose.

Fat can also produce glucose when broken down into glycerol or carbon-chain fatty acids. This is why when your carbohydrate intake goes down within the keto diet, your intake of healthy fats will increase. You can therefore continue to support your brain’s functioning, without the side-effects associated with carbohydrates, such as weight gain.

Can We Live Healthy Lives Without Eating Carbs?

When we restrict our carbohydrate intake, the “TCA” cycle, which involves the metabolization of carbohydrates into sugars and energy, is disrupted. The body begins to rely on ketogenic amino acids, which can continue to supply energy, while allowing for weight loss.

The success of the Keto diet, which champions ketogenic function, shows us it is possible to survive on fewer carbs than we may have originally assumed.

Indeed, many carb diets have been linked to a number of benefits over the years. Studies show eating fewer carbs can help people to lose weight faster than any other diet, and reduce calorie intake.

In fact, low-carb diets often prompt greater weight loss and better health benefits than most low-fat, and calorie-restricted diets. Reducing your carbohydrate intake can also help with lowering blood sugar, blood pressure, and triglycerides.

However, we may not be able to live without carbs entirely.

Even seemingly beneficial aspects of a low-carb diet, such as ketosis, can begin to have negative side effects with time. High levels of ketosis can also lead to dehydration, altered chemical balances in the blood, and problematic blood sugar levels.

Because low-carb diets struggle to provide us with the level of energy support we need, they’re typically not recommended for certain situations and people. Sticking to a very low-carb diet for long periods of time can lead to possible side effects such as:

·         Muscle loss: A study published in March 2017 found people following the keto diet for three months lost more leg muscle than people following low-fat diet.

·         Kidney issues: In ketosis, the body relies on the kidney to process a lot of nutrients. Additional pressure on the kidneys, combined with certain foods commonly consumed in the keto diet, such as red meats, can increase your chance of kidney issues.

·         Low blood sugar: Studies show while low-carb diets can help to control some blood sugar levels, it can also lead to issues such as hypoglycaemia. People with diabetes may struggle more than most when following a low-carb meal plan.

The Dangers of Eating Too Few Carbs

While there are clear benefits to low carb diets in some circumstances, cutting carbs entirely isn’t likely to be an option for most. Extremely low carb diets (such as Atkins) have been met with significant controversy over the years due to their dangerous side effects.

Notably, it’s also worth remembering carbs aren’t just a source of energy or glucose for the body. Consuming the right carbs also ensures you can provide your body with other essential substances.

Good sources of carbohydrates, such as whole grains, legumes, fruits, and vegetables are also host to various other essential “micronutrients”, such as B vitamins and phytochemicals for fighting disease. Carbs are also a source of fiber. Lacking fiber in our diets can lead to constipation, digestion issues, and nutritional deficiencies.

Research into the potential dangers of low-carb diets is also a cause for debate.

The Rush University Medical Center suggests reducing our intake of carbs can lead to a number of problems, usually after a few months. This may be why extremely low-carb diets are often only recommended as a short-term weight loss strategy.

Lowering your intake of carbohydrates could cause a number of side effects, from increased fatigue to issues with blood sugar balance, and even poor cognitive functioning. If you’re struggling to maintain enough energy, you may also find it harder to exercise and stay active, which is crucial to good health.

According to one study, extremely low-carb diets were found to increase participant’s risk of premature death. The study found the people consuming the least amount of carbs were 32% more likely to die early of any cause.

Additionally, low carb consumers were 51% more likely to die from coronary heart disease, 50% more likely to die from cerebrovascular disease, and 35% more likely to die as a result of cancer.

A study published in the Journal of Cardiology also found low intake of carbohydrates increases the risk of atrial fibrillation, a common heart rhythm issue. This condition can manifest as dizziness, fatigue, and heart palpitations.

How to Calculate Your Carbohydrate Requirements

The degree of contrasting information available on the recommended carbohydrate intake today makes it difficult to determine a one-size-fits-all number for the grams we should consume. How many grams of carbs per day could vary from person to person.

Carb requirements will differ depending on the person, and their goals, as well as genetic food sensitivities. You can find out if you have a genetic sensitivity to carbs, as well as information on the optimal diet plan for your genetic makeup, by taking a DNA test.

While it seems entirely possible to reduce your carbohydrate intake below the recommended daily allowance suggested by the USDA, it’s important to be cautious about reducing it too much.

Those following a low carb diet will need to be mindful of how their body responds to changes in nutrients, and stay wary of any significant side effects.

If you have specific medical issues, a risk of muscle loss, or diabetes, you may also need to discuss your specific carb requirements with your doctor, nutritionist or dietician.


  1. What Are the Dietary Guidelines for Americans? (Sarah Garone, NDTR)
  2. Sugar for the brain: the role of glucose in physiological and pathological brain function (Philipp Mergenthaler, Ute Lindauer, Gerald A. Dienel & Andreas Meisel)
  3. From Sugar to Fat (Laurie H. Glimcher & Ann-Hwee Lee)
  4. The Effects of a Low-Carbohydrate Diet on Appetite: A Randomized Controlled Trial (T Hu,  L Yao, K Reynolds, T Niu, S Li, P Whelton, J He & L Bazzano)
  5. Health Effects of Low-Carbohydrate Diets: Where Should New Research Go? (Judith Wylie-Rosett, EdD, RD, Karin Aebersold, MPH, Beth Conlon, MS, RD, Carmen R. Isasi, MD, PhD & Natania W. Ostrovsky, PhD)
  6. The Three-Month Effects of a Ketogenic Diet on Body Composition, Blood Parameters, and Performance Metrics in CrossFit Trainees: A Pilot Study (Wesley C. Kephart, Coree D. Pledge, Paul A. Roberson, Petey W. Mumford, Matthew A. Romero et. al)
  7. The glycaemic benefits of a very-low-carbohydrate ketogenic diet in adults with Type 1 diabetes mellitus may be opposed by increased hypoglycaemia risk and dyslipidaemia (Z Z X Leow, K J Guelfi, E A Davis, T W Jones & P A Fournier)
  8. Characteristics and Health Benefits of Phytochemicals (Claus Leitzmann)
  9. The Skinny on Low-Carb Diets (Rush System)
  11. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (The National Academies Press)
  12. Low carbohydrate diets are unsafe and should be avoided, study suggests (Science Daily)
  13. Carbohydrates (Joanne Slavin & Justin Carlson)

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