Does a Low Calorie Diet Coupled with Intermittent Fasting Lead to Weight Loss?
— By Dawn M. Sweet, Ph.D
Low calorie diets coupled with intermittent fasting have potential for helping patients with obesity to lose weight.
A Low Calorie Diet (LCD) has consistently been found to be an effective lifestyle intervention for patients with obesity. While pharmacological and surgical interventions have been effective forms of treatment for patients with obesity, lifestyle changes are also effective interventions for weight loss. New research suggests the combination of a low calorie diet and intermittent fasting may be another lifestyle intervention to consider for helping patients with obesity lose weight.1
Low Calorie Diets, Weight Loss and Body Composition
A 10 percent weight loss is the common metric for those seeking to lose weight and improve metabolic health as well as reducing the chances of developing an obesity-related disorder.1 To achieve this goal, calorie restriction, or a low calorie diet, is often a first step. A low calorie diet is divided into different stages.
Stage 1 is a four to 12 week weight reduction stage followed by a weight stabilization stage. It’s important to note that low calorie diets should be tailored to the specific needs of the patients relative to their age and sex, and low calorie diets should also be tailored to the patient’s current level of physical activity. Because weight loss is a dynamic process, adjustments can be made to the parameters of the low calorie diet. A low calorie diet is underpinned by an approach toward balanced nutrition, and the goal of a 500-800 daily kcal reduction.1 Because of their nutritional balance, meal replacements can also be used as part of low calorie diet.2
Many of the advantages associated with a low calorie diet are related to significant reductions in body mass. When a low calorie diet is used as an intervention, there is a risk of losing lean body mass in addition to fat mass, so it is important to tailor the LCD to the specific needs of the patient to minimize the risk of lean body mass. For example, in a group of women with obesity following a six-month LCD, there was a 14 percent reduction in fat mass and decreases in lean body mass ranging from 1.2-3.3 percent. Because lean body mass protects against insulin resistance, LCDs should be designed to minimize this risk.1
While weight loss can be achieved with a LCD, results are optimized when physical activity is increased. For example, in a study of sedentary men and women with obesity,3 a LCD coupled with physical activity such as brisk walking, cycling, and functional physical activity yielded a seven percent weight loss but lean body mass loss was lessened and VO2max was reduced.
Intermittent Fasting, Weight Loss and Body Composition
Intermittent fasting is characterized by cyclic eating, or time-restricted eating — eating during only certain times during the day, or eating on certain days. While the results of intermittent fasting on weight loss vary because of the type of fasting plan used, most studies have found that intermittent fasting reduces body weight and improves body composition.1 An intermittent fasting approach to weight loss does not specifically identify nutrients, so it is important to counsel patients using this approach to abide healthy eating guidelines.
Different models of intermittent fasting include alternate day eating, wherein a person eats one day and fasts the following day in an alternating pattern for a few weeks or months.4 There are also periodic models that include fasting one or two days per week. Finally, time-restricted fasting is another option that use defined “eating windows” where one can eat during a specified period.1
Intermittent fasting produces a metabolic shift can positively effect body composition. For example, as reported in a 2018 study1, research has shown that restricting eating to eight hours per day for 12 weeks resulted in a 2.6 percent weight loss for patients with obesity, which was greater than what was achieved in a matched control sample. It was also reported that patients with obesity lost 8.0 kg and reduced their waist circumference by 6.9 percent after following a 2/5 schedule (i.e. fasting for one or two days per week) for six months.
Including Low Calorie Diets and Intermittent Fasting
When medically supervised, low calorie diets have been shown to be an effective weight loss intervention for patients with obesity. Because of the nutritional value, meal replacements should be considered as part of a LCD. Like any medical intervention, its success is contingent upon patient compliance, so it is critically important for healthcare professionals to develop low calorie diet plans and intermittent fasting regimens that are tailored to each patient and realistically achievable.