Caloric restriction is a well-known method for treating obesity and related chronic diseases. However, it often proves difficult to maintain over extended periods. Intermittent fasting (IF) offers a more manageable alternative for caloric restriction, providing similar benefits such as body weight control, improved glucose homeostasis, better lipid profiles, and anti-inflammatory effects.
Understanding Intermittent Fasting
Intermittent fasting involves periods of reduced or no caloric intake, interspersed with normal eating patterns. During fasting days, dieters typically consume between 0 to 500 kcal/day. The duration of fasting can range from several hours to a full day. Common IF regimens include the 5:2 diet (two days of caloric restriction or fasting per week) and alternate-day fasting (ADF). Time-restricted feeding, another popular variant, limits energy intake to a 12 to 16-hour window each day.
The Origins of Intermittent Fasting
IF has roots in religious traditions, such as Ramadan fasting, where Muslims abstain from food during daylight hours for a month each year. Studies have shown that Ramadan fasting can have positive effects on human health.
Benefits of the 5-Day Fasting Diet Plan
A fasting-mimicking diet (FMD), developed by biogerontologist Valter Longo, mimics fasting effects while still allowing small food portions.
Weight Reduction
Weight reduction is the primary mechanism through which IF provides benefits. Similar to caloric restriction, weight loss achieved through IF reduces fasting plasma insulin levels, improves cardiovascular risk factors, and decreases body inflammatory status by regulating metabolic signaling pathways.
Read also: Comprehensive Guide to Tea Fasting
Clinical trials and reviews indicate that IF (lasting 4-24 weeks) can lead to a 4% to 10% reduction in body weight in overweight individuals. The extent of weight loss varies depending on factors like the specific dietary pattern, duration, composition, sex, and individual genetic response.
Metabolic Switch
IF induces a metabolic switch between fed and fasting states. Repetitive fasting prompts the body to shift its metabolic phase, favoring the use of ketone bodies and fatty acids over glucose. This improves metabolic flexibility, which is often impaired in obesity and type 2 diabetes. Fasting also activates autophagy and defense mechanisms against oxidative and metabolic stress, while suppressing inflammation. These effects are similar to those seen with aerobic exercise.
Fasting stimulates AMPK activity and suppresses mTOR signaling, which are important nutrient-sensing pathways. These changes inhibit FOXO-dependent gene transcription, leading to the induction of autophagy and oxidative defense mechanisms.
Glucose Homeostasis
Obesity is a major contributor to the development of type 2 diabetes (T2DM), which results from insulin resistance and oxidative stress caused by high blood glucose and free fatty acid levels. A 12-month IF trial in T2DM patients showed reductions in body weight, glycated hemoglobin levels, and fasting glucose and insulin levels. IF has a greater insulin-lowering effect than continuous caloric restriction.
In the diabetic state, IF reduces plasma concentrations of glucose and insulin and elevates adiponectin levels. However, the effect of IF on glucose homeostasis differs between diabetic and non-diabetic subjects. Studies have shown that IF may not improve insulin sensitivity in healthy, non-obese individuals and may even impair glucose tolerance in some cases.
Read also: Benefits of the Fasting Mimicking Diet
Lipid Profiles
Randomized clinical trials have demonstrated that IF improves lipid profiles related to weight reduction. IF can decrease total cholesterol, low-density lipoprotein (LDL) cholesterol, and triglycerides. These cardioprotective effects have been observed in obese adults, adolescents, and non-obese subjects. IF may also increase high-density lipoprotein (HDL) levels, although results have been mixed.
The mechanisms behind these improvements include obesity control, improved lipid profiles, elevated adiponectin levels, and a suppressed inflammatory state. Increased hepatic fatty acid oxidation during fasting reduces hepatic triglyceride accumulation, which in turn decreases VLDL production and plasma levels.
Anti-Inflammatory Effects
Systemic inflammation is linked to the pathogenesis of T2DM, cardiovascular diseases, and certain cancers. Body weight reduction decreases adipose tissue macrophages, reduces proinflammatory cytokines, and improves insulin resistance and systemic inflammatory status.
Clinical trials have shown that IF improves inflammatory status in obese subjects, reducing plasma levels of IL-6, TNF-α, CRP, and interferon-γ. However, some studies have reported inconsistent results, with IF increasing macrophage infiltration in adipose tissue in overweight or obese women.
Risks and Considerations
While IF offers several potential benefits, it also carries some risks and considerations:
Read also: Drinking Diet Coke Before Testing
Loss of Lean Body Mass and Bone Density
Some studies have reported reductions in bone density and lean body mass in participants undergoing IF. Regular IF may decrease fat-free mass more than continuous caloric restriction, although other studies have found similar losses of lean body mass between IF and CR.
Potential for Overeating
Calorie-restricted diets, including IF, can lead to a slowed metabolism and increased appetite, potentially causing overeating during non-fasting periods.
Risks for Older Adults
There is limited evidence on the benefits and effects of IF on older adults, and it could be risky in some cases, potentially leading to excessive weight loss.
Medication Interactions
Skipping meals and severely restricting calories can be dangerous for individuals taking certain medications, such as those for diabetes.
Other Potential Side Effects
Depending on the length of the fasting period, individuals may experience headaches, lethargy, crankiness, and constipation. Risks of hypoglycemia, malnutrition of proteins and vitamins, and dehydration have also been reported.
The Fast-Mimicking Diet (FMD): A Modified Approach
The fast-mimicking diet (FMD) offers the benefits of fasting without requiring complete food restriction. It involves consuming a plant-based diet that is low in calories, sugars, and protein but high in unsaturated fats for a specific period, typically 5 days per month.
How FMD Works
The FMD is designed to mimic the effects of fasting on the body without complete food restriction. It involves consuming a plant-based diet for a specific period, typically 5 days. This diet also consists of consuming:
- a low amount of calories, around 700 calories per day
- low sugars
- low protein
- high in unsaturated fats
Potential benefits of a fasting-mimicking diet based on research:
- Weight loss: FMD can lead to reductions in body weight and body fat.
- Improved metabolic health: FMD may improve markers of metabolic health, such as blood pressure, fasting glucose levels, and insulin sensitivity.
- Reduced inflammation: FMD has been shown to reduce levels of inflammatory markers like C-reactive protein (CRP).
- Lowered risk factors for age-related diseases: FMD may decrease risk factors for diseases associated with aging, such as cardiovascular disease and diabetes.
- Cellular rejuvenation: FMD can activate cellular stress response pathways and autophagy, which may promote cellular repair and rejuvenation.
- Improved cognitive function: FMD may improve cognitive function, which could be beneficial for brain health and Alzheimer’s disease prevention.
Safety Considerations and Who Should Avoid the Diet
Although the FMD offers a range of potential health benefits, it is not suitable for everyone. Individuals who are pregnant or breastfeeding, those with a history of eating disorders, and people with existing medical conditions such as diabetes, kidney disease, or heart disease, should consult with their health care provider if considering the diet. “Individuals who are considered at high risk of malnutrition or undernutrition should typically avoid fasting diet patterns,” Dr. Yaceczko warns. Additionally, those on medication should be sure to consult with a doctor before starting a fasting diet.