Obesity, defined by an elevated body mass index (BMI) due to excessive or abnormal accumulation of fat, is a global health concern. With the prevalence of obesity increasing worldwide, it has become crucial to find effective strategies for weight loss and improving metabolic health benefits. Dietary interventions are considered the first-line treatment for obese individuals, and one such strategy is intermittent energy restriction (IER).
Intermittent energy restriction involves intermittent pauses in eating, achieved through different variations such as alternate-day fasting (ADF) and time-restricted feeding (TRF). Numerous studies have shown that IER diets can be effective for weight loss and have beneficial effects on various metabolic parameters, including insulin sensitivity, lipid profile, and blood pressure. In addition, IER diets are comparable to continuous energy restriction (CER) diets in terms of weight loss and metabolic improvements.
This article aims to provide an in-depth analysis of the benefits and effects of intermittent fasting for weight loss and health. We will explore the influence of IER on body mass, fat mass, insulin sensitivity, lipid profile, gut microbiota, inflammation, hypertension, and other molecular mechanisms. We will also discuss adherence to IER diets, and potential side effects, and compare IER to CER diets. Finally, we will highlight the current limitations of knowledge on IER and suggest future directions for research in this field.
Obesity is a complex disease characterized by an elevated BMI, which is the result of excess or abnormal accumulation of fat. It is a major risk factor for various chronic conditions, including type 2 diabetes, hypertension, cardiovascular disease, and certain types of cancer. Adipose tissue, which consists of adipocytes and other cells, plays a crucial role in regulating energy balance and metabolic homeostasis. Excessive adipose tissue can lead to dysfunction and the release of inflammatory factors, contributing to insulin resistance and other metabolic disorders.
The Concept of Intermittent Energy Restriction (IER)
Dietary interventions are essential for the management of obesity, and the primary goal is caloric restriction and subsequent weight loss. Intermittent energy restriction diet (IER) or intermittent fasting is a type of diet that involves intermittent pauses in eating, achieved through different variations such as alternate-day fasting (ADF) and time-restricted feeding (TRF). ADF consists of alternating fasting days with severe energy intake restriction and subsequent feed days without caloric intake restriction. TRF involves food intake consumption within restricted hours of the day, with variations in the duration of the fasting period.
This approach to dieting has gained popularity due to its potential benefits for weight loss and metabolic health. Fasting periods during IER diets induce the expenditure of glucose and glycogen, leading to a shift in energy metabolism from glucose to fat-derived ketone bodies and free fatty acids. Fatty acids and glycerol become the main sources of energy during fasting, with the liver converting fatty acids into ketone bodies for use by the brain. Fasting also leads to improvements in glucose regulation, abdominal fat loss, and regulation of cardiometabolic parameters.
The Influence of IER on Humans
Body Mass, Fat Mass, and Ectopic Fat
Weight loss is a primary goal of dietary interventions for obesity, with a focus on reducing fat mass while preserving fat-free mass and improving body composition. Several clinical trials have demonstrated the effectiveness of IER diets, including ADF and TRF, in reducing body weight. The reduction in body weight changes among IER diet groups is commonly reported to be around 5 kg after 10-12 weeks of intervention. Shorter or longer durations of study have resulted in smaller or greater weight losses, respectively.
IER diets have also been found to induce reductions in fat mass while preserving fat-free mass. ADF diets have shown significant reductions in fat mass among obese patients. TRF diets have also been associated with reductions in body weight and fat mass among overweight individuals. In addition, IER regimens have shown potential benefits in reducing ectopic fat, which is the accumulation of fat in non-adipose tissues such as the liver and skeletal muscle.
Insulin Sensitivity and Glucose Tolerance
Obesity is often associated with insulin resistance, a condition in which the body’s cells become less responsive to insulin, leading to elevated blood glucose levels. IER diets have shown promising effects on insulin sensitivity and glucose tolerance. Studies have reported reductions in fasting insulin levels and improvements in insulin sensitivity among participants on IER regimens. Some studies have also observed reductions in fasting glucose levels among individuals following IER diets. The impact of IER on insulin and glucose levels may vary depending on factors such as sex and the timing of eating intervals.
IER regimens have been found to have beneficial effects on plasma lipid levels. Studies have reported reductions in triglyceride and LDL cholesterol levels, as well as improvements in HDL cholesterol levels. IER diets have also been associated with an increase in LDL particle size, which is important for reducing cardiovascular risk. However, the impact of IER on lipid profiles may vary depending on the specific diet and duration of intervention.
Emerging research suggests that IER diets can influence the composition of the gut microbiota, which plays a crucial role in metabolic health. Studies have found that IER, such as fasting during the Muslim holy month of Ramadan, can lead to changes in the gut microbiota, including increased levels of beneficial bacteria and improved microbial richness and diversity. These changes in the gut microbiota may contribute to the metabolic benefits observed with IER diets.
Biomarkers of Inflammation
Chronic low-grade inflammation is a common feature of obesity and is associated with various metabolic disorders. Some studies have found that IER regimens can reduce levels of inflammatory biomarkers, such as C-reactive protein (CRP), particularly in overweight and obese adults. However, the effects of IER on other inflammatory markers, such as tumour necrosis factor-α and interleukin-6, have been inconsistent.
Hypertension, or high blood pressure, is a common comorbidity of obesity and is a significant risk factor for cardiovascular disease. IER regimens have been found to have a particular ability to decrease systolic and/or diastolic blood pressure. Several studies have reported significant reductions in blood pressure among individuals following IER diets. The mechanisms through which IER lowers blood pressure are not fully understood but may involve improved vascular endothelial function.
Other Molecular Mechanisms
IER diets may influence various molecular mechanisms involved in metabolism and ageing. Animal studies have shown that IER can improve insulin sensitivity, reduce inflammation, increase stress resistance, and enhance cellular recycling processes. These effects may be mediated by the activation of specific pathways and the production of various proteins.
Adherence to IER Diets
Adherence to dietary interventions is crucial for achieving successful weight loss and metabolic improvements. Short-term studies have reported low dropout rates among individuals following IER diets. TRF diets with 8-12 hours of fasting have been well-tolerated by participants, with high compliance rates reported. Longer fasting periods have also been associated with greater adherence. Further research with longer-term interventions and follow-up is needed to assess long-term adherence to IER diets.
Side Effects of IER Diets
Side effects of IER diets are generally rare and mild. Some individuals may experience morning fatigue, headaches, changes in appetite, irritability, and dizziness during the initial days of dietary intervention. Individuals with diabetes who are on hypoglycemic drugs may be at increased risk of hypoglycemia when following IER diets. It is important to monitor blood glucose levels and adjust medication doses accordingly.
Comparison to Continuous Energy Restriction (CER) Diet
Several studies have compared the effects of IER and CER diets on weight loss and metabolic health. In most cases, both IER and CER diets are equally effective for weight loss and metabolic improvements. The daily calorie restriction in IER diets is often comparable to CER diets, with similar reductions in body weight and improvements in metabolic parameters observed. However, some studies have reported differences in weight loss between IER and CER diets, with some favouring one approach over the other. More research is needed to understand the factors that may influence the differential effects of IER and CER diets.
Alternate-Day Fasting (ADF)
Alternate-day fasting is a form of IER that involves alternating fasting days with days of normal eating. On fasting days, individuals consume only a fraction of their usual calorie intake, typically around 25% of their daily energy expenditure needs. On non-fasting days, individuals are allowed to eat freely without any specific restrictions. This pattern of fasting and feasting creates a calorie deficit that can lead to weight loss over time.
Time-Restricted Feeding (TRF)
Time-restricted feeding is another form of IER that involves limiting the daily eating window to a specific period, typically 8-10 hours. Outside of this eating window, individuals fast and consume no calories. This approach is often referred to as the 16:8 fasting method, where individuals fast for 16 hours and consume all their meals within an 8-hour window. By restricting the eating window, TRF helps to create a calorie deficit and promote weight loss.
Implementing Intermittent Energy Restriction
If you’re considering trying intermittent energy restriction as a weight loss strategy, it’s essential to approach it safely and sustainably. Here are some key tips to keep in mind:
Consult a Healthcare Professional
Before embarking on any dietary changes, it’s crucial to consult with a healthcare professional, especially if you have any underlying health conditions or are taking medication. They can provide personalised guidance and ensure that intermittent energy restriction is suitable for you.
Choose the Right IER Method
There are various forms of intermittent energy restriction, so it’s essential to choose the method that aligns with your lifestyle and preferences. Whether you opt for alternate-day fasting or time-restricted feeding, select an approach that you can adhere to in the long term.
Plan Your Meals
Proper meal planning is key to success with intermittent energy restriction. On fasting days, ensure that you have low-calorie, nutrient-dense foods readily available. On non-fasting days, focus on consuming a balanced diet consisting of carbohydrates, proteins and fats that meet your nutritional needs. Dietary education from a qualified dietitian may be useful.
During fasting periods, it’s crucial to stay hydrated. Drink plenty of water throughout the day to support your overall health and well-being. Hydration can also help curb hunger pangs and keep you feeling satisfied.
Listen to Your Body
Pay attention to how your body responds to intermittent energy restriction. If you experience any adverse effects or discomfort, adjust your approach accordingly. It’s essential to prioritise your health and well-being above all else.
Intermittent energy restriction (IER) diets, such as alternate-day fasting (ADF) and time-restricted feeding (TRF), have emerged as effective strategies for weight loss, weight management and improving metabolic health. These diets have been found to reduce body weight, and body fat, and improve insulin sensitivity, lipid profile, and blood pressure. Adherence to IER diets is generally high, and side effects are rare and mild. IER diets have been compared to continuous energy restriction (CER) diets and have shown similar effectiveness in promoting weight loss and metabolic improvements. However, further research is needed to understand the long-term effects and safety of IER diets, as well as the specific populations that may benefit the most from this approach. Overall, IER diets offer a viable alternative for individuals who may struggle with traditional continuous dietary restrictions.
- The Role of Intermittent Energy Restriction Diet on Metabolic Profile and Weight Loss among Obese Adults – PMC
- Intermittent energy restriction: a novel weight loss approach for adolescents – American Society for Nutrition
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