Low-carbohydrate (low-carb) diets have emerged as a popular strategy for weight loss and managing certain health conditions since 1860, and more recently, in 1972. Today, interest in low-carb approaches continues to grow. While all low-carbohydrate approaches reduce the overall intake of carbohydrates, there is no clear consensus on what defines a low-carb diet. Studies have defined low carbohydrate as a percent of daily macronutrient intake or total daily carbohydrate load.
Understanding Low-Carb Diets
Low-carb diets involve reducing carbohydrate intake while increasing the consumption of proteins and fats. There are 3 macronutrients-carbohydrates (4 kcal/g), fat (9 kcal/g), and protein (4 kcal/g)-found in food. When carbohydrates are restricted, the body primarily uses fat as its energy source, leading to various metabolic changes and potential health benefits.
Defining "Low-Carb"
The definition of a low-carb diet can vary. Here's a breakdown of carbohydrate intake levels:
- Very low-carbohydrate: Less than 10% of total calories from carbohydrates, or 20 to 50 grams per day.
- Low-carbohydrate: Less than 26% of total calories from carbohydrates, or less than 130 grams per day.
- Moderate-carbohydrate: 26% to 44% of total calories from carbohydrates.
- High-carbohydrate: 45% or greater of total calories from carbohydrates.
The Institute of Medicine recommends that Americans obtain 45% to 65% of their calories from carbohydrates.
How Low-Carb Diets Work
Low-carb approaches stem primarily from the hypothesis that lowering insulin, a critical hormone that produces an anabolic, fat-storing state, improves cardiometabolic function, and induces weight loss. This approach has been recently called the carbohydrate-insulin model. When reducing carbohydrates from the diet, the macronutrient intake of fat and protein generally increases to compensate for the reduction of carbohydrates. Studies have shown low-carb approaches superior to other dietary methods in producing rapid weight loss for the first 6 to 12 months. While diets inducing weight loss produce a caloric deficit, the mechanism of low-carb diets remains debated.
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One hypothesis supporting why low-carb approaches produce rapid weight loss compared to other diets is that fats and protein increase satiety and produce less concomitant hypoglycemia. This increase in satiety and less rebound hypoglycemia reduces hunger and overall food intake and produces a caloric deficit. Another hypothesis contends that low-carb diets can produce a higher metabolic burn than high-carb diets. Recent studies show a metabolic advantage of approximately 200 to 300 more calories burned compared to an isocaloric high-carb diet. However, these theories remain controversial.
Ketogenic Diet: A Specific Low-Carb Approach
The ketogenic (keto) diet, a specific low-carb version, deserves mention. Keto diets restrict carbohydrates to induce nutritional ketosis and typically limit carbs to 20 to 50 grams daily. Restricting carbs to under 50 grams induces glycogen depletion and ketone production by mobilizing fat stored in adipose tissue. Nutritional ketosis produces ketone bodies (acetoacetate, acetone, and beta-hydroxybutyrate) and is measurable as serum or urinary ketones. Nutritional ketosis generally increases serum ketones from 1 mmol/L to 7 mmol/L but does not produce metabolic acidosis. Diabetic ketoacidosis, by definition, includes metabolic acidosis, hyperglycemia, and serum ketones (generally over 20 mmol/L).
Net Carbs
The term net carbs refers to the total amount of fully digestible carbohydrates contained in a meal. Net carbs are calculated by subtracting the whole amount of fiber and half the amount of sugar alcohols from the amount of total carbs. The nutritional impact of using net carbs is to help the patient choose foods that are higher in fiber.
Benefits of Low-Carb Diets
Despite the debate, numerous systematic reviews demonstrate that low-carb diets are as effective, if not more effective, for weight loss compared to other diets. Low-carb diets have been associated with several health benefits. People often use them to support weight loss and manage blood sugar levels.
Weight Loss
Most research on low-carb approaches has shown that a low-carb diet, specifically a ketogenic diet, induces rapid weight loss induction. Initial weight loss is due partly to water loss, but fat loss occurs with adherence to the low-carb approach. With all dietary interventions, as adherence to the diet wanes, the weight loss effect becomes similar to other nutritional approaches after one year. Notably, most low-carb diet studies generally use an ad-libitum approach to caloric intake (limiting carbs instead), while most comparison diets are calorie-restricted. High-protein diets can help you stay full after eating and lower cravings, which can help you lose weight. But some of the short-term weight loss is often due to losing water from cutting out carbs.
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A ketogenic diet can help you lose slightly more weight than a low fat diet. This often happens with less hunger. One review of 13 studies found that following a very low carb, ketogenic diet was slightly more effective for long-term weight loss than a low fat diet. People who followed the keto diet lost an average of 2 pounds (0.9 kg) more than the group that followed a low fat diet. Another study in 34 older adults found that those who followed a ketogenic diet for 8 weeks lost nearly five times as much total body fat as those who followed a low fat diet. The increased ketones, lower blood sugar levels, and improved insulin sensitivity may also play a key role.
Blood Sugar Control
Before medications, carbohydrate control has been the cornerstone of glycemic control in type 1 and type 2 diabetes. Dietary carbohydrates increase insulin needs, and reduction of carbohydrate intake can improve glycemic control. A recent study demonstrated a significant reduction of insulin and oral medications and hemoglobin A1c reduction with ketogenic approaches while demonstrating a high adherence to the intervention at 12 months. Also, markers of cardiometabolic risk factors improved.
Low-carb diets can help you control your blood sugar levels and manage diabetes and prediabetes. A systematic review and meta-analysis found low-quality evidence that low-carb approaches increase type 2 diabetes remission and are generally safe. Approaches to nutritional lifestyle and approaches to diabetes medical nutrition therapy have included a low-carb approach as an option in recent guidelines. Recent prospective and randomized controlled trials have consistently benefited glycemic control, weight loss, and sustained medication reduction using a very low-carb approach, less than 14% of energy from carbohydrates.
The ketogenic diet can boost insulin sensitivity and cause fat loss, leading to significant health benefits for people with type 2 diabetes or prediabetes. One older study found that the ketogenic diet improved insulin sensitivity by a whopping 75%. A small study in women with type 2 diabetes also found that following a ketogenic diet for 90 days significantly reduced levels of hemoglobin A1C, which is a measure of long-term blood sugar management. Another study in 349 people with type 2 diabetes found that those who followed a ketogenic diet lost an average of 26.2 pounds (11.9 kg) over a 2-year period. This is an important benefit when considering the link between weight and type 2 diabetes. What’s more, they also experienced improved blood sugar management, and the use of certain blood sugar medications decreased among participants throughout the course of the study.
Maintaining and Building Muscle
While some diets can lead to reduced muscle mass, you can maintain and build muscle while losing weight by increasing your protein intake. Encouraging higher protein loads to support physical activity can also help improve body composition and metabolic adaptations.
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Other Health Benefits
Studies have now shown that the diet can have benefits for a wide variety of different health conditions:
- Heart disease. The ketogenic diet can help improve risk factors like body fat, HDL (good) cholesterol levels, blood pressure, and blood sugar.
- Cancer. The diet is currently being explored as an additional treatment for cancer, because it may help slow tumor growth.
- Alzheimer’s disease. The keto diet may help reduce symptoms of Alzheimer’s disease and slow its progression.
- Epilepsy. Research has shown that the ketogenic diet can cause significant reductions in seizures in epileptic children.
- Parkinson’s disease. Although more research is needed, one study found that the diet helped improve symptoms of Parkinson’s disease.
- Polycystic ovary syndrome. The ketogenic diet can help reduce insulin levels, which may play a key role in polycystic ovary syndrome.
- Brain injuries. Some research suggests that the diet could improve outcomes of traumatic brain injuries.
Concerns and Risks
Several theoretical concerns about the long-term safety of low-carb diets deserve mention.
Nutritional Ketosis vs. Ketoacidosis
Nutritional ketosis can be induced in the keto diet, the induction phase, and when carb load is limited to less than 10% of macronutrient intake or 20 to 50 g/d of carbohydrates. However, there is no evidence that very low-carb intake produces metabolic ketoacidosis and remains safe in patients, even those with type 2 diabetes. While there have been cases of diabetic ketoacidosis (DKA) with concomitant SGLT2 inhibitors in patients with type 2 diabetes, it is unclear if the very low-carb approach increases the risk of DKA with SGLT2 use.
A type of medication called sodium-glucose cotransporter 2 (SGLT2) inhibitors for type 2 diabetes can increase the risk for diabetic ketoacidosis, a dangerous condition that increases blood acidity. Anyone taking this medication should avoid the keto diet.
Mortality
Several studies link low-carb diets to increased mortality. Epidemiological studies and meta-analyses have shown an increased mortality risk with a carbohydrate intake of less than 40%. However, the recent Prospective Urban Rural Epidemiology (PURE) study, a large prospective nutrition study involving over 135,000 participants across the globe, found a relationship between increased mortality and higher carbohydrate intake and lower mortality associated with higher fat intake. Another prospective cohort study found that healthy low-carb and low-fat diets were associated with lower mortality, and unhealthy low-carb and low-fat diets were associated with higher mortality. This suggests that the quality of the food matters, not just the level of macronutrient intake.
Cholesterol Levels
Incorporating more fat and protein in response to reducing dietary carbs has led to concerns about the effect of low-carb dieting on lipids, specifically LDL cholesterol. Some protein sources - such as fatty cuts of meat, whole dairy products, and other high-fat foods - can raise cholesterol, increasing your chance of heart disease. However, studies showed that people on the Atkins diet for up to two years actually saw a drop in “bad” cholesterol levels.
Renal Function
With a potentially higher protein intake on low-carb diets, some have expressed concerns about renal function. However, depending on specific goals, athletes should ingest protein loads to optimize muscle protein synthesis (1.6 g/kg) or endurance sports (0.8 g/kg). No data generally associates high-protein load with worsening kidney function in those with normal kidney function. To prevent further renal deterioration, a low-protein or very-low-protein diet (0.2-0.8 g/kg/d) may be recommended for those with chronic kidney disease.
If you have any kidney problems, eating too much protein puts added strain on your kidneys. This could worsen kidney function. Certain groups should avoid high-protein, low-carb diets due to related health risks, Derocha says. She suggests avoiding a high-protein, low-carb diet if you have certain conditions and health issues, such as: Kidney disease or kidney issues, as too much protein strains your kidneys.
Nutrient Deficiencies
Because carbohydrates include many food groups (like fruits and vegetables), you face a higher risk of missing out on certain nutrients when you cut carbs, Derocha says. A properly planned low carb diet plan should include a large amount of non-starchy vegetables.
Osteoporosis and Kidney Stones
When you’re on a high-protein diet, you may urinate more calcium than normal. There are conflicting reports, but some experts think this could make osteoporosis and kidney stones more likely.
Other Risks
Certain groups should avoid high-protein, low-carb diets due to related health risks, Derocha says. She suggests avoiding a high-protein, low-carb diet if you have certain conditions and health issues, such as: History of disordered eating or eating disorders, as low-carb diets promote restrictive eating; Pregnancy or breastfeeding, as nutrient-dense diets are critical during these stages; Constipation concerns, as a low-carb, high-protein diet can lower your fiber intake and lead to constipation.
Getting Started with a Low-Carb Diet
As patients with type 2 diabetes improve glycemic control, lower weight, and reduce medication use, hemoglobin A1c may fall below the threshold for diagnosis. After a shared decision-making process with the patient, there are numerous ways to start a patient on a low-carb diet. Low-carb nutrition may be advisable for those who desire healthy or athletic performance, weight loss, improvement of glycemic control for type 1 or 2 diabetes, or a seizure disorder.
First, understanding macronutrients and their relation to food is critical to patient counseling. Secondly, determine the patient's desire for either small steps or a rapid induction phase through motivational interviewing and S.M.A.R.T (specific, measurable, attainable, realistic, and time-bound) goal setting. Limiting added sugar (sucrose) and refined carbohydrates is critical in improving food quality and will generally reach a moderate carbohydrate (<45% carbohydrates) level.
One method to initiate low-carb is through a rapid induction phase of 2 to 4 weeks, with 20 to 50 grams of carbohydrates to induce nutritional ketosis. Ad libitum vegetables that grow above the ground and are lower in carbohydrate content are encouraged. If limited initially or during the induction phase, full-fat dairy, legumes, and whole grains can also be added during this maintenance phase as long as goals are maintained and tolerated without any hypersensitivity or an adverse response. The lifelong maintenance phase can then continue per patient preference. Patients on chronic medications may require rapid medication adjustments while on a low-carbohydrate diet. Recently a small randomized controlled study demonstrated improved glycemic control and reduction of medication use led by a community-based clinical pharmacist.
If you want to start a high-protein, low-carb diet, you should first talk to your doctor and go over any health concerns. According to Grace Derocha, RDN, CDCES, Spokesperson for the Academy of Nutrition and Dietetics, here are some ways to get started:
- Stock your house with high-protein, low-carb foods such as fish, lean meat, red meat, eggs, cheese, broccoli, kale, and spinach.
- Get high-protein, low-carb snacks, such as string cheese, hard-boiled eggs, and Greek yogurt, as many go-to snack foods aren’t high in protein.
- Stay hydrated, especially because removing fruit from your diet can lower your water intake, as many fruits contain water.
- Look at menus before eating out and research takeout options.
- Setting realistic and sustainable goals that you can stick with. “Make small adjustments that don’t take over your whole life to set yourself up for success,” Derocha says. “Remember that food is more than fuel for your body and find ways you can still enjoy it and incorporate it into your traditions, celebrations, and social gatherings.”
Foods to Eat
You should base the majority of your meals around these foods:
- Meats: Red meat, steak, ham, sausage, bacon, chicken, and turkey
- Fatty fish: Salmon, trout, tuna, and mackerel
- Eggs: Pastured or omega-3 whole eggs
- Butter and cream: Grass-fed butter and heavy cream
- Cheese: Unprocessed cheeses like cheddar, goat, cream, blue, or mozzarella
- Nuts and seeds: Almonds, walnuts, flaxseeds, pumpkin seeds, chia seeds, etc.
- Healthy oils: Extra virgin olive oil, and avocado oil
- Avocados: Whole avocados or freshly made guacamole
- Low carb veggies: Green veggies, tomatoes, onions, peppers, etc.
- Condiments: Salt, pepper, herbs, and spices
Some examples of high-protein, low-carb foods include: Meats, including poultry, fish, and red meat (heart-healthy options such as salmon, mackerel, anchovies, sardines, and herring, Derocha says); Eggs; Healthy fats and oils such as avocados and olive oil; Low-carb vegetables such as broccoli, kale, spinach, and cucumbers; Cheese; Nuts; Cauliflower rice; Beans, legumes, and lentils; Greek yogurt; Tofu and tempeh; Lower-carb fruits such as raspberries and blackberries. Lower-carb fruits should be a part of the ketogenic lifestyle. Examples of low-carb fruits are raspberries, blackberries, strawberries, watermelon, cantaloupe, kiwi, peaches, clementines, and grapefruit. Vegetables contain fewer carbs, lower calories, and higher fiber than fruits. They are packed with phytonutrients, vitamins, and minerals, and are an important part of any healthy diet.
Foods to Avoid
Here’s a list of foods that need to be reduced or eliminated on a ketogenic diet:
- Sugary foods: Soda, fruit juice, smoothies, cake, ice cream, candy, etc.
- Grains or starches: Wheat-based products, rice, pasta, cereal, etc.
- Fruit: All fruit, except small portions of berries or strawberries
- Beans or legumes: Peas, kidney beans, lentils, chickpeas, etc.
- Root vegetables and tubers: Potatoes, sweet potatoes, carrots, parsnips, etc.
- Low fat or diet products: Low fat mayonnaise, salad dressings, and condiments
- Some condiments or sauces: Barbecue sauce, honey mustard, teriyaki sauce, ketchup, etc.
- Unhealthy fats: Processed vegetable oils, mayonnaise, etc.
- Alcohol: Beer, wine, liquor, mixed drinks
- Sugar-free diet foods: Sugar-free candies, syrups, puddings, sweeteners, desserts, etc.
Depending on your daily carb allowance, you might need to limit or avoid the following foods: Sweet snacks: candy, ice cream, baked goods, other products that contain added sugar; Refined grains: white rice, white pasta, tortillas, crackers; Diet and low fat products: including dairy products, cereals, or crackers that are low in fat but contain added sugar; Highly processed foods: convenience meals, fast food, cookies, chips, pretzels; Sugar-sweetened beverages: soda, sweet tea, sports drinks, energy drinks.
Sample Meal Plan
This is a sample menu for 3 days on a low carb diet plan. That said, ask a doctor or dietitian what carbohydrate allowance works best for you based on your health goals and personal preferences.
Day 1
- Breakfast: 2 slices sprouted Ezekiel bread with 1/2 avocado, salt, and pepper. Total carbs: 36.5 g.
- Lunch: 3 ounces (oz) (85 g) grilled chicken with 2 cups (340 g) zucchini noodles made with 1 clove of garlic, butter, and 1 oz (28 g) Parmesan. Total carbs: 17 g.
- Dinner: bunless burger with a slice of Cheddar cheese, served with 1/2 cup (78 g) cooked broccoli and 2 tablespoons (35.7 g) of salsa. Total carbs: 8.5 g.
- Total carbs for the day: 62 g
Day 2
- Breakfast: 7 oz (200 g) plain Greek yogurt with 1/4 cup (37 g) blueberries and 1 oz (28.35 g) almonds. Total carbs: 19.4 g.
- Lunch: 3 oz (85 g) rib eye roast with 1/2 cup (120 g) mashed rutabaga and 1 cup (129 g) sautéed green beans. Total carbs: 13.5 g.
- Dinner: 3 oz (85 g) baked salmon with 1/2 cup (90 g) cooked asparagus and 3/4 cup (85 g) cauliflower rice. Total carbs: 7.7 g.
- Total carbs for the day: 40.6 g
Day 3
- Breakfast: breakfast bowl with 2 large hard-boiled eggs, 1 tomato, and 1 cup cubed avocado. Total carbs: 19 g.
- Lunch: 2.5 cups (244 g) shrimp garden salad with shrimp, lettuce, eggs, tomato, and carrots, with 2 tablespoons (tbsp), or 30 milliliters (mL), olive oil vinaigrette. Total carbs: 10.5 g.
- Dinner: 3 oz (85 g) grilled chicken with 1/2 cup (78 g) roasted Brussels sprouts and 1/2 cup (93 g) cooked quinoa. Total carbs: 25.2 g.
- Total carbs for the day: 54.7 g
Healthy Low-Carb Snacks
If you get hungry between meals, here are some healthy, easy-to-prepare, low carb snacks that can fill you up: a piece of fruit; Greek yogurt; one or two hard-boiled eggs; baby carrots; leftovers from the previous night; a handful of nuts; some cheese and meat.
Dining Out on a Low-Carb Diet
Following a low carb diet while dining out can be challenging. Not only are the portion sizes often very large, but some restaurant foods are served with condiments, sauces, or side dishes that are high in added sugar or carbs. Still, at most restaurants, making your meals low carb is fairly easy. Here are a few tips to get started: Opt for a meat- or fish-based main dish. Choose plain water instead of sugary soda or fruit juice. Get extra vegetables or a side salad instead of bread, potatoes, or rice. Check the menu beforehand to find options that fit your daily carb allowance. Ask for sauces, condiments, or dressings on the side so you can control your portion sizes. Consider taking half of your meal “to go” to reduce the amount of carbs during your restaurant meal.
When eating out, select a meat-, fish-, or egg-based dish. Order extra veggies instead of carbs or starches, and have cheese for dessert. At Mexican restaurants, you can enjoy any type of meat with extra cheese, guacamole, salsa, and sour cream. For dessert, ask for a mixed cheese board or berries with cream.
Potential Side Effects
Although the ketogenic diet is usually safe for most healthy people, there may be some initial side effects while your body adapts. There’s some anecdotal evidence of these effects often referred to as the keto flu. Based on reports from some on the eating plan, it’s usually over within a few days. Reported keto flu symptoms include diarrhea, constipation, and vomiting. Other less common symptoms include: poor energy and mental function; increased hunger; sleep issues; nausea; digestive discomfort; decreased exercise performance.
To minimize this, you can try a regular low carb diet for the first few weeks. This may teach your body to burn more fat before you completely eliminate carbs. A ketogenic diet can also change the water and mineral balance of your body, so adding extra salt to your meals or taking mineral supplements may help. Talk to your doctor about your nutritional needs. At least in the beginning, it’s important to eat until you’re full and avoid restricting calories too much. Usually, a ketogenic diet causes weight loss without intentional calorie restriction.
Many of the side effects of starting a ketogenic diet can be limited. Easing into the diet and taking mineral supplements can help.
Supplements
Although no supplements are required, some can be useful.
- MCT oil. Added to drinks or yogurt, MCT oil provides energy and helps increase ketone levels.
- Minerals. Added salt and other minerals can be important when starting out due to shifts in water and mineral balance.
- Caffeine. Caffeine can have benefits for energy, fat loss, and performance.
- Exogenous ketones. This supplement may help raise the body’s ketone levels.
- Creatine. Creatine provides numerous benefits for health and performance. This can help if you are combining a ketogenic diet with exercise.
- Whey. Use half a scoop of whey protein in shakes or yogurt to increase your daily protein intake.
Is a Low-Carb Diet Right for You?
Low-carb diets can be a powerful tool for the treatment of excess weight. In addition to helping with weight reduction, a low carb diet can be helpful in treating conditions such as diabetes and sleep apnea.
Key Considerations
- Consult your doctor: Everyone responds differently to nutrition plans, and you should always talk to your doctor before starting any new diet. They can help you come up with a plan that will make sure you’re getting enough fruits and vegetables, and that you’re getting lean protein foods.
- Focus on whole foods: Base the majority of your diet on whole, single-ingredient foods. It’s not all meats and fats. Order this and replace any high carb food with extra vegetables.
- Long-term sustainability: Remember, weight loss that lasts is usually based on changes you can live with for a long time, not a temporary diet.
Vegetarian Low-Carb Diet
You can follow a low carb diet as a vegetarian, but it can be more challenging because most plant-based protein foods also contain carbs. It’s important to ensure you’re getting enough calories and nutrients, so consulting with your doctor or a registered dietician is a good idea.
Low-Carb Diet for Diabetes
Research shows that following a low carb diet while living with diabetes can help you manage the disease. Eating low carb with diabetes is similar to eating low carb without diabetes. You can generally eat and avoid the same foods. That said, you’ll need to track your blood sugar and follow the diabetes treatment prescribed by your doctor.