Many people are interested in trying a low-carbohydrate diet because they've heard it promotes weight loss. While some evidence supports the eating plan for this purpose, a lack of carbohydrates is associated with some adverse health effects such as ketosis and a heightened cardiovascular risk.
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The USDA's Dietary Guidelines for Americans says that carbohydrates should comprise 45 to 65 percent of your daily caloric intake. According to the Mayo Clinic, this means that, of a standard 2,000-calorie diet, 900 to 1,300 calories, or 225 to 325 grams, should come from carbohydrates. Eating less than this amount may result in a carbohydrate deficiency.
Effects of Low-Carbohydrate Consumption
Rush University Medical Center describes what happens when people follow a low-carbohydrate diet. After eating carbohydrates, whatever isn't used immediately for energy is stored in the muscles as glycogen or converted into fat in the liver.
During physical activity, the body first uses glycogen for energy, but if insufficient carbohydrates have been consumed, glycogen reserves are depleted. Consequently, since the body can't get the glycogen it needs for fuel, it starts to break down protein in muscles to use as energy.
After a few months on a low-carbohydrate diet, particularly for people with an active lifestyle, the effects become dangerous, states Rush. Metabolism slows, fat storage builds and the risk of fatigue, dehydration and muscle aches increases. For this reason, individuals who exercise regularly shouldn't follow a diet that severely restricts carbohydrates. If they don't eat enough of these foods, they won't have the energy to do their workouts.
Carbohydrate Deficiency and Ketosis
The ultimate low-carbohydrate diet is the ketogenic diet, otherwise called the keto diet. It involves drastically reducing carbohydrate consumption to 5 to 10 percent of the daily calorie intake and getting most of the calories from fat and some protein, says the University of Texas M.D. Anderson Cancer Center.
In carbohydrate deprivation, the liver transforms fat into acids called ketones, which the body uses for fuel. This process, referred to as ketosis, normally begins after three or four days of restricting carbohydrates.
Read more: Why Do I Feel Weak on the Ketogenic Diet?
Early weight loss on the keto diet is due to the loss of water weight associated with depletion of glycogen, notes M.D. Anderson. After a few days, people may experience short-term unpleasant effects, such as nausea, fatigue and dizziness, which are a cluster of symptoms called the keto flu.
Over time, ketosis may result in dehydration, altered chemical balance in the blood and perilously low blood sugar levels. Other long-term effects are unclear, but lack of fiber intake can cause constipation and nutritional deficiencies can result from low consumption of fruits, vegetables and whole grains.
Because of health concerns that may stem from the keto diet, certain people shouldn't attempt the diet. These include those with liver failure, pancreatitis and disorders of fat metabolism, reports a March 2019 study published in StatPearls. Consult with your doctor before starting the diet.
Despite short-term weight loss, very little evidence supports the keto diet's long-term efficacy and safety, asserts the Mayo Clinic. Harvard Health Publishing recommends that, instead of following an eating plan that severely restricts carbohydrates or other nutrients, you adopt a well-balanced healthy diet that is rich in fruits, vegetables, whole grains, nuts, seeds, fish, lean meats and olive oil. An example of this type of eating is the Mediterranean diet.
Carbohydrate Deficiency and Mortality Risk
The body of scientific research isn't conclusive, but a few studies indicate that a lack of carbohydrates in the diet may be linked to a higher risk of mortality. In a 2013 study featured in PLOS One, researchers reviewed investigations to determine the long-term effects of a low-carbohydrate diet. The results showed that, although the eating plan wasn't linked to an elevated heart risk, it was associated with a significantly raised risk of all-cause mortality.
A March 2019 study published in the Journal of the American College of Cardiology found that a low-to-moderate intake of carbohydrates increases the risk of atrial fibrillation (AF), a common heart rhythm disorder. AF manifests as fatigue, dizziness and palpitations and can lead to a stroke or heart attack. The authors concluded that doctors shouldn't extensively recommend low-carbohydrate diets for weight loss.
Functions of Carbohydrates
Carbohydrates, one of the primary components of a healthy diet, are categorized into three types: starches, sugars and fiber, states a November 2014 article published in Advances in Nutrition. Because of their functions, they're profoundly important.
Digestion turns sugars and starches into glucose, which serves as the sole energy source for red blood cells and a primary energy source for the brain and central nervous system. Glucose is also stored as glycogen in muscles.
Fiber, the part of carbohydrates not broken down, has multifaceted functions. According to MedlinePlus, two of the primary ones are weight management and satiety, which is a feeling of fullness. Insoluble fiber helps promote healthy bowel movements, and soluble fiber reduces cholesterol and improves blood glucose regulation.
Carbohydrate Food List
Carbohydrates are a source of confusion because they can be categorized in different ways. It's good to know the different types, as well as which ones are beneficial and which ones are unhealthy.
Starchy carbohydrates include:
- Starchy vegetables like potatoes and corn
Sugar carbohydrates comprise:
- Natural sugars in fruit and milk
- Corn syrup
- Brown sugar
- White sugar
Fiber carbohydrates are:
This category also includes whole grains, such as:
- Grown rice
- Foods made of whole-grain flours
The American Heart Association makes the distinction between simple and complex carbohydrates. Simple carbs, which should be avoided, include:
- Table sugar
Complex carbs are:
- Starchy vegetables
- Whole grains
While fruits, vegetables and whole grains are healthy carbohydrates, refined grains are unhealthy carbohydrates. These include:
- White rice
- Baked goods made with white flour such as cookies, cakes, muffins and crackers
- Mayo Clinic: "Carbohydrates: How Carbs Fit Into a Healthy Diet"
- Rush University Medical Center: "The Skinny on Low-Carb Diets"
- University of Texas M.D. Anderson Cancer Center: "What You Need to Know About the Ketogenic Diet"
- Mayo Clinic: "The Truth Behind the Most Popular Diet Trends of the Moment"
- PLOS One: "Low-Carbohydrate Diets and All-Cause Mortality: A Systematic Review and Meta-Analysis of Observational Studies"
- Journal of the American College of Cardiology: "U-Shaped Relationship Between Carbohydrate Intake Proportion and Incident Atrial Fibrillation"
- MedlinePlus: "Carbohydrates"
- Centers for Disease Control and Prevention: "More About Carbs"
- American Heart Association: "Carbohydrates"
- StatPearls: "Ketogenic Diet"
- Harvard Health Publishing: "Ketogenic Diet: Is the Ultimate Low-Carb Diet Good for You?"
- Health.gov: "Dietary Guidelines for Americans, 2015-2020: Appendix 7. Nutritional Goals for Age-Sex Groups Based on Dietary Reference Intakes and Dietary Guidelines Recommendations"
- Advances in Nutrition: "Carbohydrates"