Low-carbohydrate diets have gained popularity as a strategy for weight loss and managing certain health conditions. However, very low carbohydrate diets, which severely restrict carbohydrate intake, can have significant side effects. This article explores the potential benefits and drawbacks of very low carbohydrate diets, including ketogenic diets and the early phases of the Atkins Diet, to provide a comprehensive understanding of their impact on health.
What Happens When You Cut Carbs?
Carbohydrates are essential nutrients that the body converts into glucose, or blood sugar, to provide energy. When carbohydrate intake is drastically reduced, as in very low-carb diets like the keto diet or the initial phase of the Atkins Diet, the body enters a state called nutritional ketosis. During ketosis, the liver starts producing ketones by breaking down fat, which serves as an alternative fuel source when glucose is limited.
How Low is Low-Carb?
To induce nutritional ketosis, very low-carb diets typically restrict carbohydrate intake to less than 10% of total macronutrient intake, which translates to about 20 to 50 grams of carbs per day. Low-carb diets generally aim for less than 26% of nutritional intake, or 130 grams of carbs.
Potential Benefits of Very Low Carbohydrate Diets
Weight Loss
A sudden reduction in carbs can lead to rapid weight loss, primarily due to the loss of water weight. When carb intake decreases, the body depletes its glycogen stores in the muscles. Glycogen helps the body retain water, so when it's used up, water is excreted. Additionally, the body may lose some salt along with the carbs. However, this water weight tends to return when carbohydrate consumption resumes. It typically takes two to three weeks for ketosis to ramp up and start burning fat.
Improved Glycemic Control
For individuals with diabetes and insulin resistance, low-carbohydrate diets can be beneficial in achieving glycemic control. Cutting carbs, especially refined carbs and sugars, can aid in blood sugar management.
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Cardiovascular Health Improvements
Decreasing carb intake may improve heart health. Very low carb diets have been shown to decrease blood triglyceride levels, which can increase your chance of heart disease.
Reduction of Belly Fat
Limited research indicates that very-low-carb diets are better than low fat diets at decreasing belly fat, a type of fat associated with inflammation and certain diseases.
Management of Epilepsy
The ketogenic diet has been used for about 100 years to treat epilepsy, particularly in children who do not respond to medication. This approach requires close medical supervision, frequent lab checks, and urine tests.
Potential for Managing Other Neurological Conditions
Research has indicated the keto diet may help improve neurological conditions such as Alzheimer’s disease, autism and brain cancers such as glioblastoma.
Side Effects of Very Low Carbohydrate Diets
While very low carbohydrate diets may offer some benefits, they can also cause several adverse effects:
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The "Keto Flu"
Ketosis can lead to symptoms such as weakness, fatigue, dizziness, and headaches, collectively known as the "keto flu." More severe side effects can include stomach pain, nausea, and vomiting. Some healthcare professionals believe these symptoms result from inadequate nutrient intake from fruits, beans, vegetables, and whole grains, which are often restricted on keto diets.
Brain Fog and Sleep Disturbances
As the body adjusts to lower blood sugar levels, individuals may experience brain fog. Initially, sleep disturbances can also occur, leading to further fatigue and cognitive impairment.
Digestive Issues
Low-carb diets are often low in fiber, which can cause constipation. While this usually resolves within a few weeks, it can be uncomfortable. Additionally, gas can become trapped in the digestive tract, causing bloating and pain. Staying well-hydrated and consuming adequate electrolytes (minerals that help balance body water and nourish cells) can help mitigate these symptoms.
Halitosis (Bad Breath)
When the body uses fatty acids instead of carbs for fuel, it releases ketones, including acetone, through the breath. This can result in a fruity or sweet odor, sometimes described as smelling like decaying apples. Dehydration can also contribute to bad breath by reducing saliva production, which is essential for clearing bacteria and food particles from the mouth.
Hypoglycemia (Low Blood Sugar)
Very low-carb diets can lower blood sugar levels, which can be beneficial for individuals with diabetes. However, true ketosis carries the risk of hypoglycemia, where blood sugar levels drop too low. The standard treatment involves consuming 15 grams of carbs to raise blood sugar. If levels remain low after 15 minutes, another 15 grams are needed. People with diabetes should monitor their blood sugar frequently and be prepared to adjust their medications accordingly.
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Cardiovascular Concerns
Very low-carb diets tend to be high in fat, potentially increasing the risk of heart disease. Saturated fat intake should be limited to no more than 5% to 6% of total intake, with a focus on healthy fats from sources like avocados, olives, and nuts. While these diets may improve triglyceride and HDL (“good”) cholesterol levels, they can also raise LDL, or “bad” cholesterol, which is a risk factor for heart disease.
Mood Changes
Drastically reducing healthy carbs, which provide sugar to the brain, can lead to mood swings and irritability. Studies have shown that individuals on long-term low-carb diets may have lower serotonin levels in their brains, potentially increasing the risk of anxiety and depression.
Liver Strain
On a low-carb diet, the liver processes more fat, which can exacerbate existing liver conditions.
Kidney Problems
Nutritional ketosis may increase uric acid levels, potentially leading to kidney stones or gout flares. Some studies suggest that individuals with mild chronic kidney disease can follow a keto diet under close medical supervision, while others indicate that diets high in red meat and low in whole grains, low-fat dairy, and fruit can increase the risk of kidney disease.
Nutritional Deficiencies
A no-carb diet may not provide enough vitamins and minerals, such as potassium, B vitamins, and vitamin C, which are abundant in fruits, vegetables, and other plant foods. Additionally, the increased urination that results from restricting carbs may lead to nutrient deficiencies such as sodium and potassium over time.
Constipation
Since a no-carb diet restricts fruits, most vegetables, beans, and whole grains, it can be very low in fiber, which helps digestion by helping maintain bowel regularity. Because of this, a no-carb diet may lead to constipation.
Long-Term Effects and Sustainability
The long-term consequences of very low carbohydrate diets are not well-established. Observational studies suggest that both low-carbohydrate (less than 40% of energy from carbohydrates) and very high-carbohydrate diets (more than 70% of energy from carbohydrates) are associated with increased mortality. Concerns about potential nutritional deficiencies and their impact on renal function have been raised, highlighting the need for further investigation into the sustainability and long-term health outcomes of extreme dietary patterns.
Who Should Avoid Very Low Carbohydrate Diets?
Due to the restrictive nature and potential risks, very low-carb diets are not suitable for everyone. They are not appropriate for:
- Individuals with eating disorders
- Children
- Cholesterol hyper-responders
- Pregnant or nursing women
It is crucial to consult with a healthcare professional before starting a very low-carb diet, especially for individuals with pre-existing health conditions.
Foods to Eat and Avoid on a No-Carb Diet
A no-carb diet focuses on foods high in protein and fat. Here’s a breakdown of what’s typically allowed and what’s restricted:
Foods Allowed:
- Meat and low carb animal products: chicken, beef, turkey, lamb, venison, bison, pork, eggs, butter, lard, cheese
- Seafood: salmon, tilapia, cod, shrimp, sardines, herring, crab
- Seasonings: herbs and spices
- Zero-calorie beverages: water, black coffee, and plain tea
- Nuts and seeds (those low in net carbs): almonds, walnuts, pumpkin seeds, sunflower seeds, pistachios, cashews
- Non-starchy vegetables (those low in net carbs): broccoli, zucchini, bell peppers, cauliflower, leafy greens, rutabaga, turnips, Brussels sprouts, asparagus, mushrooms
- High fat fruits: coconut, avocado
Foods to Avoid:
- Grains: rice, farro, barley, quinoa, wheat, bread, pasta
- Sweets and baked goods: cakes, cookies, candy, sodas, sugary drinks
- Fruits: apples, oranges, bananas, berries, kiwi, pears
- Starchy vegetables: peas, corn, squash, potatoes
- Beans and legumes: black beans, kidney beans, chickpeas, lentils
- Dairy: milk and yogurt
- Condiments with added sugar: ketchup, barbecue sauce, salad dressings
- Alcohol: beer, wine, liquor, sugary mixed drinks
Sample Five-Day Menu for a No-Carb Diet
Here is a sample five-day menu for a no-carb diet:
Day 1
- Breakfast: eggs, bacon, sliced avocado
- Lunch: romaine lettuce with ground turkey, cheese, and olive oil dressing
- Dinner: salmon, zucchini noodles, side of sunflower seeds
- Snacks: beef jerky, cheese
Day 2
- Breakfast: eggs, steak, bell pepper strips
- Lunch: tuna-fish lettuce wraps, carrots dipped in mashed avocado
- Dinner: lamb chops, spinach salad with walnuts, and olive oil dressing
- Snacks: hard-boiled eggs, pistachios
Day 3
- Breakfast: eggs, turkey sausage, avocado
- Lunch: scallops, Brussels sprouts roasted with Parmesan cheese
- Dinner: pork chops, roasted tomatoes, and turnips
- Snacks: sunflower seeds, brie
Day 4
- Breakfast: eggs with shredded chicken, jalapeño, cheddar cheese
- Lunch: turkey burger patties with rutabaga fries
- Dinner: meatballs and zucchini noodles with roasted tomatoes
- Snacks: sardines, macadamia nuts
Day 5
- Breakfast: cheesy eggs with broccoli, chicken sausage
- Lunch: flank steak and arugula salad with olive oil dressing, cashews
- Dinner: coconut-crusted shrimp, roasted asparagus, and mushrooms
- Snacks: turkey jerky, avocado
Meta-Analysis of Low-Carbohydrate Diets in Overweight/Obese Individuals with Type 2 Diabetes Mellitus
A meta-analysis was conducted to assess the effects of low-carbohydrate diets on glucose and lipid metabolism in overweight or obese adults with Type 2 Diabetes Mellitus (T2DM). The analysis included randomized controlled trials (RCTs) with participants aged 18 or older diagnosed with T2DM, comparing low-carbohydrate diets to any other diet. The outcomes measured changes in HbA1c, total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglycerides (TG), with a minimum intervention duration of 8 weeks.
Results
The meta-analysis included 17 studies with a total of 1197 participants (643 in the experimental groups and 554 in the control groups). The results showed a significant reduction in HbA1c levels in participants adhering to low-carbohydrate diets compared to those on control diets (MD = -0.36, 95% CI -0.44 to -0.29, p < 0.00001).
Furthermore, the analysis revealed beneficial changes in lipid profiles associated with low-carbohydrate diets, including a significant reduction in triglyceride levels (MD = -19.91, 95% CI [-28.83, -10.99], p < 0.00001) and a significant increase in HDL-C levels (MD = 2.49, 95% CI [1.07, 3.91], p = 0.0006).
Low-carbohydrate diets also resulted in substantial reductions in body weight (MD = -3.71, 95% CI [-5.85, -1.58], p < 0.05), body mass index (BMI) (MD = -0.85, 95% CI [-1.59, -0.11], p < 0.05), diastolic blood pressure (DBP) (MD = -2.44, 95% CI [-3.69, -1.18], p < 0.05), and waist circumference (MD = -3.84, 95% CI [-4.98, -2.70], p < 0.05).
Adverse Reactions
Among the included articles, 12 studies addressed adverse reactions. The types of mild adverse events (AEs) reported included asthenia, headache, nausea, and vomiting. There was a higher incidence of adverse events related to hypoglycemia, with 14 instances of hypoglycemic symptoms and seven documented hypoglycemic events. In terms of other adverse events, six cases of constipation, two cases of diarrhea, and four cases of abdominal discomfort were clearly documented. In the low-carbohydrate diet group, serum uric acid levels demonstrated an increasing trend post-intervention, potentially elevating the risk of gout attacks.
Conclusion of Meta-Analysis
The meta-analysis suggests that low-carbohydrate diets can be effective in managing T2DM, particularly in overweight and obese individuals, by improving glycemic control, lipid profiles, body weight, and blood pressure. However, potential adverse reactions, such as hypoglycemia and gastrointestinal issues, should be carefully monitored.