The ketogenic diet, a low-carbohydrate, high-fat eating plan, has gained popularity as a weight-loss strategy. However, many individuals experience increased hunger when transitioning to or maintaining a low-carb diet. This article explores the potential causes of hunger on a low-carb diet, strategies for managing it, and the diet's long-term effects on appetite and overall health.
What is the Keto Flu?
The "keto flu" is a real phenomenon experienced by some individuals when they drastically reduce their carbohydrate intake. It mimics flu-like symptoms as the body adapts to using fat for fuel instead of glucose. Symptoms generally begin within the first one or two days of carbohydrate restriction, but may last a week or less. In extreme cases it may last up to a month but depending on genetics, some may never experience the keto flu.
Managing Keto Flu:
- Ease into the Diet: Gradually reduce carb intake instead of making sudden, drastic changes.
- Hydration: Drink plenty of water to combat headaches and boost energy levels. A general recommendation is to drink a minimum amount of ounces of water every day equal to half of your current body weight.
- Electrolytes: Replenish electrolytes like salts, potassium, and magnesium, which are often depleted on a low-carb diet.
- Healthy Fats: Consume adequate healthy fats to help the body transition to burning fat for fuel.
- Sleep: Take Epsom salt baths or drink keto-friendly herbal tea to relax muscles and improve sleep.
- Light Exercise: Engage in light exercise to relieve muscle pain and tension.
Appetite and Macronutrient Composition
The relationship between dietary macronutrient composition and appetite is complex and has been a topic of debate. Manipulating the macronutrient content of the diet, particularly restricting carbohydrates and fats, has been used extensively for weight loss and weight control. It's unclear whether weight loss due to restrictions in either carbohydrate or fat results from changes in appetite or appetite-related hormones. Appetite is influenced by both behavioral and biological characteristics, with various peptides synthesized and released from the gastrointestinal tract acting as important regulators.
Ghrelin, secreted from the stomach, functions as an appetite signal that increases hunger, stimulates food intake, and decreases fat utilization in adipose tissue. Peptide YY, released from the distal small intestine and colon after meals, reduces appetite by increasing satiety. Weight loss increases appetite-stimulating hormones like ghrelin and decreases satiety hormones like PYY.
Low-Carbohydrate Diets and Appetite
Low-carbohydrate diets have been effective for weight loss and weight management. Previous studies provide some evidence that these diets may reduce appetite measured by self-report, while a few small studies have shown the opposite. A recent meta-analysis concluded that ketogenic low-carbohydrate diets reduce appetite slightly from baseline measures, but comparison with a non-ketogenic diet as a control group was not possible due to the small number of studies with such control groups which met inclusion criteria. The mechanisms of potential reduction in appetite are unclear but may involve appetite-related hormones. Data on the effects of carbohydrate restriction on appetite-related hormones are scarce, limited to a few small, short-term studies.
Read also: Strategies for Diet Control
Study on Macronutrient Composition and Appetite Hormones
One study examined whether the macronutrient composition of weight-loss diets affects appetite and its regulation, as reflected in levels of appetite hormones, and to what degree these effects are independent of weight loss itself. The study involved 148 adults with a body mass index of 30-45 kg/m2, who were free of diabetes, cardiovascular disease, and chronic kidney disease at baseline. Participants were randomly assigned to either a low-carbohydrate diet (carbohydrate [excluding dietary fiber] <40 g/day; N=75) or a low-fat diet (<30% energy from fat, <7% from saturated fat; N=73).
Participants in both groups attended individual and group dietary counseling sessions where they were provided the same behavioral curriculum and advised to maintain baseline levels of physical activity. Appetite and appetite-related hormones were measured at 0, 3, 6, and 12 months of intervention.
Key Findings:
- At 12 months, peptide YY levels decreased in both groups, but to a lesser extent in the low-carbohydrate group than in the low-fat group.
- Mean differences in changes in ghrelin between the two groups were not statistically significant throughout the study.
- Approximately 99% of dietary effects on peptide YY are explained by differences in dietary macronutrient content.
- A low-fat diet reduced peptide YY more than a low-carbohydrate diet.
The findings suggest that satiety may be better preserved on a low-carbohydrate diet compared to a low-fat diet.
Other Studies and Findings
Several studies have examined the effects of low-carbohydrate diets on appetite-related hormones. One study involving obese diabetic patients showed a marginal increase in ghrelin levels on a low-carbohydrate diet. Another study found no significant differences between low-fat and low-carbohydrate diets in changes in fasting peptide YY. These trials had very small sample sizes and relatively short follow-up periods.
Data from the Optional Macronutrient Intake Trial to Prevent Heart Disease (OMNI-Heart) examined the effects of diets rich in different macronutrients but did not test a typical low-carbohydrate diet for weight loss. In contrast, the study mentioned above tested the effects of a typical low-carbohydrate diet for weight loss, limiting carbohydrate intake to less than 40 grams per day, without setting specific energy goals for the consumption of protein and fats, and compared it to a widely recommended low-fat diet.
Read also: Exploring the Carnivore Diet
Limitations and Strengths of Research
Research on the effects of low-carbohydrate diets on appetite and related hormones has some limitations. Appetite is often assessed using a single question, lacking details on various aspects such as hunger and satiety. Some studies assess only ghrelin and peptide YY, but not other appetite-related hormones. Clinical trials may not be powered to test appetite-related hormones. Self-reported dietary information may be subject to recall issues.
However, studies also have strengths, including the assessment of both appetite-related hormones and self-reported appetite measurements. Data are collected by trained and certified staff using rigorous quality control protocols. Furthermore, some studies include a substantial proportion of black participants, a group underrepresented in previous trials, which makes the examination of race differences possible.
Practical Considerations of Low-Carb Diets
Following a very high-fat diet may be challenging to maintain. Some negative side effects of a long-term ketogenic diet have been suggested, including an increased risk of kidney stones and osteoporosis, and increased blood levels of uric acid (a risk factor for gout). Possible nutrient deficiencies may arise if a variety of recommended foods on the ketogenic diet are not included. It is important to not solely focus on eating high-fat foods but to include a daily variety of the allowed meats, fish, vegetables, fruits, nuts, and seeds to ensure adequate intakes of fiber, B vitamins, and minerals (iron, magnesium, zinc)-nutrients typically found in foods like whole grains that are restricted from the diet.
Available research on the ketogenic diet for weight loss is still limited. Most of the studies so far have had a small number of participants, were short-term (12 weeks or less), and did not include control groups.
Ketogenic Diet: A Deeper Dive
The ketogenic diet is a low-carbohydrate, fat-rich eating plan used for centuries to treat specific medical conditions. In the 19th century, it was used to control diabetes, and in 1920 it was introduced as an effective treatment for epilepsy in children. Today, it is gaining attention as a potential weight-loss strategy.
Read also: Safety of Low-Carb Diets During Lactation
How It Works
The premise of the ketogenic diet for weight loss is that if you deprive the body of glucose-the main source of energy for all cells, obtained by eating carbohydrate foods-an alternative fuel called ketones is produced from stored fat. The brain demands a steady supply of glucose, about 120 grams daily, because it cannot store glucose. During fasting or when very little carbohydrate is eaten, the body first pulls stored glucose from the liver and temporarily breaks down muscle to release glucose. If this continues for 3-4 days and stored glucose is fully depleted, blood levels of insulin decrease, and the body begins to use fat as its primary fuel. The liver produces ketone bodies from fat, which can be used in the absence of glucose. When ketone bodies accumulate in the blood, this is called ketosis. Healthy individuals naturally experience mild ketosis during periods of fasting (e.g., sleeping overnight) and very strenuous exercise. Proponents of the ketogenic diet state that if the diet is carefully followed, blood levels of ketones should not reach a harmful level (known as “ketoacidosis”) as the brain will use ketones for fuel, and healthy individuals will typically produce enough insulin to prevent excessive ketones from forming. The rate at which ketosis happens and the number of ketone bodies that accumulate in the blood vary from person to person and depend on factors such as body fat percentage and resting metabolic rate.
Ketoacidosis
Excessive ketone bodies can produce a dangerously toxic level of acid in the blood, called ketoacidosis. During ketoacidosis, the kidneys begin to excrete ketone bodies along with body water in the urine, causing some fluid-related weight loss. Ketoacidosis most often occurs in individuals with type 1 diabetes because they do not produce insulin, a hormone that prevents the overproduction of ketones. However in a few rare cases, ketoacidosis has been reported to occur in nondiabetic individuals following a prolonged very low carbohydrate diet.
Macronutrient Ratios
There is not one “standard” ketogenic diet with a specific ratio of macronutrients (carbohydrates, protein, fat). The ketogenic diet typically reduces total carbohydrate intake to less than 50 grams a day-less than the amount found in a medium plain bagel-and can be as low as 20 grams a day. Generally, popular ketogenic resources suggest an average of 70-80% fat from total daily calories, 5-10% carbohydrate, and 10-20% protein. For a 2000-calorie diet, this translates to about 165 grams fat, 40 grams carbohydrate, and 75 grams protein. The protein amount on the ketogenic diet is kept moderate in comparison with other low-carb high-protein diets, because eating too much protein can prevent ketosis.
Foods to Eat and Avoid
Many versions of ketogenic diets exist, but all ban carb-rich foods. Some of these foods may be obvious: starches from both refined and whole grains like breads, cereals, pasta, rice, and cookies; potatoes, corn, and other starchy vegetables; and fruit juices. Some that may not be so obvious are beans, legumes, and most fruits. Most ketogenic plans allow foods high in saturated fat, such as fatty cuts of meat, processed meats, lard, and butter, as well as sources of unsaturated fats, such as nuts, seeds, avocados, plant oils, and oily fish. Strong emphasis on fats at each meal and snack to meet the high-fat requirement. Some dairy foods may be allowed. Although dairy can be a significant source of fat, some are high in natural lactose sugar such as cream, ice cream, and full-fat milk so they are restricted. Protein stays moderate. Certain fruits in small portions like berries. Fruits other than from the allowed list, unless factored into designated carbohydrate restriction.
Net Carbs
“Net carbs” and “impact carbs” are familiar phrases in ketogenic diets as well as diabetic diets. They are unregulated interchangeable terms invented by food manufacturers as a marketing strategy, appearing on some food labels to claim that the product contains less “usable” carbohydrate than is listed. Net carbs or impact carbs are the amount of carbohydrate that are directly absorbed by the body and contribute calories. They are calculated by subtracting the amount of indigestible carbohydrates from the total carbohydrate amount. Indigestible (unabsorbed) carbohydrates include insoluble fibers from whole grains, fruits, and vegetables; and sugar alcohols, such as mannitol, sorbitol, and xylitol commonly used in sugar-free diabetic food products. However, these calculations are not an exact or reliable science because the effect of sugar alcohols on absorption and blood sugar can vary. Some sugar alcohols may still contribute calories and raise blood sugar. The total calorie level also does not change despite the amount of net carbs, which is an important factor with weight loss.
Short-Term Benefits
The ketogenic diet has been shown to produce beneficial metabolic changes in the short-term. Along with weight loss, health parameters associated with carrying excess weight have improved, such as insulin resistance, high blood pressure, and elevated cholesterol and triglycerides. There is also growing interest in the use of low-carbohydrate diets, including the ketogenic diet, for type 2 diabetes.
Research on Ketogenic Diets and Weight Loss
A meta-analysis of 13 randomized controlled trials following overweight and obese participants for 1-2 years on either low-fat diets or very-low-carbohydrate ketogenic diets found that the ketogenic diet produced a small but significantly greater reduction in weight, triglycerides, and blood pressure, and a greater increase in HDL and LDL cholesterol compared with the low-fat diet at one year.
A systematic review of 26 short-term intervention trials (varying from 4-12 weeks) evaluated the appetites of overweight and obese individuals on either a very low calorie (~800 calories daily) or ketogenic diet (no calorie restriction but ≤50 gm carbohydrate daily) using a standardized and validated appetite scale. None of the studies compared the two diets with each other; rather, the participants’ appetites were compared at baseline before starting the diet and at the end. Despite losing a significant amount of weight on both diets, participants reported less hunger and a reduced desire to eat compared with baseline measures. The authors noted the lack of increased hunger despite extreme restrictions of both diets, which they theorized were due to changes in appetite hormones such as ghrelin and leptin, ketone bodies, and increased fat and protein intakes. The authors suggested further studies exploring a threshold of ketone levels needed to suppress appetite; in other words, can a higher amount of carbohydrate be eaten with a milder level of ketosis that might still produce a satiating effect? This could allow inclusion of healthful higher carbohydrate foods like whole grains, legumes, and fruit.
A study of 39 obese adults placed on a ketogenic very low-calorie diet for 8 weeks found a mean loss of 13% of their starting weight and significant reductions in fat mass, insulin levels, blood pressure, and waist and hip circumferences. Their levels of ghrelin did not increase while they were in ketosis, which contributed to a decreased appetite. However during the 2-week period when they came off the diet, ghrelin levels and urges to eat significantly increased.
A study of 89 obese adults who were placed on a two-phase diet regimen (6 months of a very-low-carbohydrate ketogenic diet and 6 months of a reintroduction phase on a normal calorie Mediterranean diet) showed a significant mean 10% weight loss with no weight regain at one year. The ketogenic diet provided about 980 calories with 12% carbohydrate, 36% protein, and 52% fat, while the Mediterranean diet provided about 1800 calories with 58% carbohydrate, 15% protein, and 27% fat. Eighty-eight percent of the participants were compliant with the entire regimen.
Potential Risks and Considerations
Following a very high-fat diet may be challenging to maintain. Some negative side effects of a long-term ketogenic diet have been suggested, including increased risk of kidney stones and osteoporosis, and increased blood levels of uric acid (a risk factor for gout). Possible nutrient deficiencies may arise if a variety of recommended foods on the ketogenic diet are not included. It is important to not solely focus on eating high-fat foods, but to include a daily variety of the allowed meats, fish, vegetables, fruits, nuts, and seeds to ensure adequate intakes of fiber, B vitamins, and minerals (iron, magnesium, zinc)-nutrients typically found in foods like whole grains that are restricted from the diet.
Do the diet’s health benefits extend to higher risk individuals with multiple health conditions and the elderly? As fat is the primary energy source, is there a long-term impact on health from consuming different types of fats (saturated vs. unsaturated)?