Milly Gaines
Calorie restriction involves reducing daily caloric intake below what is typical without malnutrition or deprivation of essential nutrients. Fasting diets, such as time-restricted feeding, alternate-day fasting, and the 5:2 diet, are a form of calorie restriction where a person severely limits intake during certain times. Calorie restriction has been shown to have health benefits in animal studies, including improved metabolism, longer life spans, and delayed onset of age-associated diseases. In humans, calorie restriction has been shown to lower the risk of multiple degenerative conditions and improve health markers. However, extreme calorie restriction can lead to impaired immune function and malnutrition, causing negative health effects.
| Characteristics | Values |
|---|---|
| Definition | Calorie restriction involves reducing average daily caloric intake without malnutrition or deprivation of essential nutrients. |
| Purpose | To improve health, slow aging, and increase lifespan. |
| Types | Time-restricted feeding, alternate-day fasting, and the 5:2 diet. |
| Results | Lower blood pressure, improved lipid profile, reduced oxidative damage, reduced inflammation, improved insulin sensitivity, lower fasting glucose levels, and reduced weight. |
| Precautions | May not be safe or feasible for people who are not overweight, including older adults. Should be done under the supervision of a dietitian to ensure proper nutrition. |
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What You'll Learn
Calorie restriction and fasting
Calorie Restriction
Calorie restriction aims to reduce average daily calorie intake without malnutrition or deprivation of essential nutrients. It is based on the idea that maintaining a low-normal body weight can improve health and slow aging. Research in animals has shown that calorie-restricted diets can increase lifespan by up to 30% while reducing the incidence of age-related disorders and chronic diseases. In humans, calorie restriction has been linked to a reduced risk of degenerative conditions and improved markers of health, including lower blood pressure, improved lipid profiles, and reduced inflammation.
It's important to note that extreme calorie restriction, such as a 40% reduction in calories, can lead to impaired immune function and negative side effects. Therefore, it is generally recommended to work with a dietitian to ensure proper nutrition and make each calorie count. Some baseline health checks, such as blood work to assess cholesterol and blood glucose levels, can also help track improvements. Gradual changes, such as substituting refined carbs for healthy fruits and vegetables, are often suggested.
Fasting
Fasting involves completely abstaining from food or severely limiting calorie intake during specific time intervals. There are various types of fasting regimens, including time-restricted feeding, where meals are consumed within a limited number of hours (e.g., 6-8 hours) each day, and alternate-day fasting. Intermittent fasting can be combined with overall calorie restriction and specific dietary patterns, such as the Mediterranean diet, to promote long-term health. Observational studies have found that individuals who routinely fast for religious or other reasons tend to have lower rates of clogged arteries and coronary artery disease. However, these studies do not control for other factors, such as diet quality or nutritional supplement use.
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Health benefits
Calorie restriction diets have been associated with a range of potential health benefits, although it is important to note that most of the research in this area has been conducted on animals, and more long-term human studies are needed to confirm these effects.
One of the key health benefits of calorie restriction is its potential to slow the ageing process and increase longevity. Animal studies have shown that calorie restriction can delay the onset of age-related disorders and extend lifespan. For example, research on rats and mice has indicated that a restricted-calorie diet may increase lifespan by nearly 30%. Similar results have been found in studies on rhesus monkeys, which are genetically similar to humans. These studies suggest that calorie restriction can reduce the incidence of age-related conditions such as cancer, heart disease, and diabetes.
In humans, observational studies suggest that calorie restriction can promote weight loss and may lower the risk of certain diseases, including diabetes, heart disease, and stroke. Additionally, a study of moderate calorie restriction in humans led to the identification of a gene involved in improved immune and metabolic functions, suggesting that calorie restriction may have broader health benefits beyond weight management.
Calorie restriction has also been found to improve specific health markers. For example, one study found that calorie restriction led to changes in gene activity in body fat and associated immune cells, inhibiting the activity of the Pla2g7 gene, which regulates inflammation. This suggests that calorie restriction may improve immune function and reduce inflammation, potentially enhancing healthy lifespan.
It is important to note that extreme calorie restriction can have adverse health effects, including impaired immune function and an increased risk of malnutrition. Therefore, it is crucial to work with a healthcare professional when considering a calorie restriction diet to ensure that it is done safely and in combination with other healthy lifestyle factors, such as regular exercise and a balanced diet.
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Longevity
Calorie restriction (CR) diets have been a topic of interest for scientists since 1935, when a Cornell scientist, Clive McCay, discovered that rats on a calorie-restricted diet lived nearly 30% longer than those on normal diets. Since then, research has shown that CR diets can extend the lifespan of various animals, including worms, crabs, snails, fruit flies, rodents, rhesus monkeys, and dogs.
CR diets involve reducing average daily caloric intake below what is typical, without malnutrition or deprivation of essential nutrients. Fasting diets, which may result in fewer calories, are sometimes included under the umbrella of CR diets. In a fasting diet, a person may not eat at all or severely limits their intake during certain times of the day, week, or month. Time-restricted feeding is a form of intermittent fasting where meals are consumed within a limited number of hours (e.g., 6-8 hours) each day, with no consumption during the remaining hours.
Observational studies have compared people who routinely fast for religious or other reasons to those who do not fast, and found that those who fast routinely are less likely to have clogged arteries or coronary artery disease. However, these studies do not control for other factors that could affect results, such as diet quality or use of nutritional supplements.
In humans, CR diets have been found to lower the risk of multiple degenerative conditions and improve medical markers of health. CR reduces the risk of chronic diseases, including cancer, diabetes, heart disease, obesity, and Type 2 diabetes, and delays biological aging. Studies show that individuals on CR diets have greater insulin sensitivity, lower blood pressure, improved lipid profiles, reduced oxidative damage, and reduced markers of inflammation. CR diets have also been found to reduce body weight and fat mass, which can contribute negatively to some health conditions.
While CR diets have shown potential for improving health and longevity, they are not without their challenges. CR diets can be difficult to maintain long-term, and there is a risk of malnutrition if the diet is not properly designed to include essential nutrients. Extreme caloric restriction, such as a 40% reduction in calories, is associated with impaired immune function and negative physical and psychological effects, as seen in the Minnesota Starvation Experiment.
Overall, while CR diets may offer potential benefits for longevity and health, more research is needed to fully understand their effects on humans and to determine safe and feasible long-term dietary regimens.
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Weight loss
Calorie restriction does not mean malnutrition or deprivation of essential nutrients. In fact, it is important to ensure that a calorie-restricted diet includes all the necessary nutrients, as malnutrition can have serious negative effects on the body, as seen in the Minnesota Starvation Experiment. This study showed that a group of lean men who restricted their calorie intake by 45% for six months experienced metabolic adaptations such as decreased body fat, but also negative effects such as anemia, edema, and muscle wasting. Therefore, it is important to ensure that a calorie-restricted diet is properly planned and includes a variety of nutrient-dense foods.
To lose weight, one must achieve a calorie deficit, which means consuming fewer calories than one burns. Calorie-restricted diets facilitate this deficit by reducing the number of calories consumed. This can be achieved through various methods, such as time-restricted feeding, where meals are consumed within a limited number of hours each day, or intermittent fasting, where individuals fast for a set period of time, usually between 16 and 24 hours, and then eat normally during the remaining hours or days. These methods of calorie restriction have been shown to be effective for weight loss and improving various health markers.
For example, a study on the effects of calorie restriction in humans, called the CALERIE trial, showed that participants who reduced their calorie intake by an average of about 14% over two years experienced a reduction in cardiometabolic risk factors, including cholesterol, blood pressure, and weight. Additionally, an observational study found that individuals who routinely fasted were less likely to have clogged arteries or coronary artery disease, indicating that calorie restriction may have cardiovascular benefits.
It is important to note that calorie restriction may not be suitable for everyone, and it is always recommended to consult with a healthcare professional or dietitian before starting any new diet. Additionally, while calorie restriction can be an effective tool for weight loss, it is important to ensure that the diet is properly planned and includes a variety of nutritious foods to avoid potential negative health consequences.
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Risks and side effects
Restricting calories can have several risks and side effects, and it is important to consult a healthcare provider before making any significant changes to your diet. Calorie restriction may not be suitable for everyone, and certain groups, such as pregnant or breastfeeding women, children, teens, and older adults, should approach very low-calorie diets with caution or avoid them altogether.
One of the main risks associated with calorie restriction is malnutrition, as a restricted diet may not provide all the essential nutrients required by the body. This can lead to metabolic adaptations, such as a decrease in body fat, improved lipid profile, and a reduced resting heart rate. However, it can also result in negative effects, including anemia, edema, muscle wasting, weakness, dizziness, irritability, lethargy, and depression.
Calorie restriction can also impact fertility and reproductive function, particularly in women. Studies have shown that reduced calorie intake can suppress reproductive function in women, leading to irregular menstrual cycles or their absence. Additionally, insufficient calorie intake may reduce estrogen levels, negatively affecting bone and heart health.
Another potential side effect of calorie restriction is an increased risk of infections and illnesses, especially when combined with high levels of physical activity. This may be due to the body's weakened immune system, which can be a result of not getting enough nutrients, such as vitamin A.
Furthermore, very low-calorie diets can lead to minor side effects such as fatigue, constipation, nausea, and diarrhea. These conditions usually improve within a few weeks and are rarely a cause for concern. However, gallstones are a more serious potential side effect, as rapid weight loss can cause the liver to secrete more cholesterol, which can combine with bile and form gallstones.
While calorie restriction has been shown to have potential benefits, such as reducing risk factors for cardiovascular disease and diabetes, more research is needed to fully understand the long-term effects and risks associated with this dietary approach.
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Frequently asked questions
Calorie restriction involves reducing average daily caloric intake below what is typical or habitual, without malnutrition or deprivation of essential nutrients.
Studies have shown that calorie restriction can reduce the risk of chronic diseases, such as cancer, diabetes, heart disease, obesity, and Type 2 diabetes, and delays biological aging in humans.
Calorie-restricted diets can take many forms, such as time-restricted feeding, alternate-day fasting, and the 5:2 diet. In general, they involve reducing food intake without causing malnutrition.
Calorie restriction is not practical for most people and it is difficult to maintain long-term. It is important to consult with a dietitian before starting any new diet to ensure it is safe and appropriate for your individual needs.
Extreme caloric restriction—a 40% reduction in calories—is associated with impaired immune function, which can lead to more severe infections. Additionally, there is a risk of malnutrition if the diet is not carefully planned to include essential nutrients.
