Exercise Timing For Healthy Weight Loss
By Paulina Monge, student of Clinical Nutrition at the Francisco Marroquín University.
The purpose of the review is to determine the effect of the timing of exercise on healthy weight loss. Controversy exists on the timing of exercise for greater weight loss. There is a controversy between exercising in a fed vs. fasted state and between short bouts vs. continuous exercise throughout the day and when is it the best time to workout. In regards to the first point, there is still controversy if fasting or a fed state is the best approach for weight loss, however, fed exercising could lead to a healthier weight loss diminishing the loss of muscle and the ability to exercise at a higher intensity. The benefits of exercising in bouts instead of continuous are small but significant. Lastly exercising in the morning showed benefits for weight loss when compared to afternoon exercise, however, more studies are needed.
El propósito de esta revisión es determinar el efecto del tiempo para hacer ejercicio en la pérdida de peso saludable. Existe controversia en qué tiempo es mejor hacer ejercicio para la mayor pérdida de peso. Existe controversia entre hacer ejercicio alimentado o en ayunas, controversia entre sesiones cortas o continuo a lo largo del día de ejercicio y cuándo es el mejor momento para hacer ejercicio. Con respecto al primer punto, todavía existe controversia sobre si el ayuno o el estado de alimentación es el mejor enfoque para perder peso, sin embargo, el ejercicio alimentado podría conducir a una pérdida de peso más saludable, disminuyendo la pérdida de músculo y la capacidad de hacer ejercicio a una mayor intensidad. Los beneficios de hacer ejercicio en turnos en lugar de continuo son pequeños pero significativos. Por último, hacer ejercicio por la mañana mostró beneficios en la pérdida de peso en comparación con el ejercicio por la tarde, sin embargo, se necesitan más estudios.
overweight, obesity, fasting, timing of exercise, fat mass, fat free mass, muscle
sobrepeso, obesidad, ayuno, tiempo para el ejercicio, masa grasa, masa libre de grasa, músculo
Exercise is defined as planned, structured and repetitive physical activity that has as a final or intermediate objective the improvement or maintenance of physical fitness . Weight loss can often be the objective of exercise, especially in a time of rapid prevalence increase of overweight and obesity. In the United States it is estimated that 1 out of every 2 adults will have obesity by the year 2030; the most current data about the United States obesity prevalence was 42.4% in 2017 – 2018 . The growing obesity epidemic as it is estimated that 39% of the adult worldwide population is overweight or has obesity .
Obesity is a risk factor for multiple cardiovascular diseases such as cardiac arrhythmias, coronary heart disease, heart failure, stroke and ventricular dysfunction; for which the American Heart Association has recommended weight loss. It is also associated with insulin resistance, type 2 diabetes, dyslipidemia, pulmonary disease, hypertension and inflammation. Multiple comorbidities described before have shown improvement with weight loss. As such exercise and high physical activity which encourage weight loss should be part of the integral treatment for obesity. The American College of Sports Medicine recommendations of physical activity for different goals are shown on Table 1. Besides benefits in the cardiovascular system and on metabolic health, exercise induces adaptations to skeletal muscle that promotes muscle mass and muscle function. Studies in the last few years have found that exercise could have beneficial effects in the adipose tissue; as it increases the presence of “beige” cells; such studies have been done in rodents. “Beige” cells are a type of subcutaneous white adipose cell that has high plasticity and with stimuli produced by exercise among other factors, can mimic the characteristics of brown adipose tissue which is more metabolically active . Additionally, this type of adipose tissue could be linked to a greater feeling of being full . A weight-loss approach that exclusively uses a reduced-calorie diet decreases both lean mass and fat mass therefore, the importance of exercise in weight reduction plans is evident .
However, the question stands: what factors or conditions around exercise result in greater healthy weight loss and promotion of positive changes in body composition? Healthy weight loss is defined as weight loss that avoids the loss of lean mass or its function as it promotes the loss of fat mass; avoiding the risk of sarcopenia. In people living with obesity with a weight loss goal, physical activity should be promoted to maintain muscle mass, and improve muscle strength and physical function . Fat loss occurs when fats, specifically triglycerides, are released into the bloodstream as free fatty acids to be transported to the tissue where energy is needed. When blood flow increases to the active muscles more free fatty acids are delivered, they get inside the mitochondria where fatty acid oxidation occurs . The mobilization and oxidation of fat components reduce the size of the adipose tissue which is reflected in body weight and body composition.
Weight loss and exercise in a fasted vs. fed state
Fasting is characterized by the absence of energy intake for a prolonged period of time; most people’s daily fast consists of 8 to 12 hrs which is the time they sleep. During fasting there are reduced levels of insulin and hepatic glycogen; this promotes ketone bodies to be used as a predominant energy source. Thus, when performing exercise in a fasted state greater utilization of fat as energy substrate is observed. Greater lipolysis doesn’t mean greater loss of fat mass or adipose tissue because if the fatty acid oxidation rate doesn’t increase simultaneously the broken down fat can not be used as energy and becomes adipose tissue again. Ferreira et al. In a meta-analysis comparing the effects of aerobic exercise in fasted versus fed state on fat metabolism found that there was a significant increase in fat oxidation in mostly moderate-intensity aerobic exercise performed in the fasted state (95 % CI −5·38, −0·79; I2 39·1 %; p < 0.001). This same study showed no significant difference in the free fatty acid concentrations between the two groups . However, this study was missing research on the effects of each intervention in the following 24 hours. Imayama et al. did evaluate the 24-hour oxidation of exercise before breakfast compared to sedentarism in 9 young female subjects and found that exercise performed overnight fasting increases 24-hour oxidation when compared to sedentarism (p < 0.01) . Research is still needed to compare the effect of fasted versus fed exercise on 24-hour fatty acid oxidation.
Hackett et al. In a meta-analysis to analyze the effect of governing fasted exercise on weight loss and body composition found that, performing aerobic exercise at medium and high intensity at a fasted state did not influence weight loss or changes in fat or lean mass when compared to a fed state (95 % CI −0.59, 0.66; p = 0.91). The results of this study could have been affected by not having a weight loss environment or plan besides exercise . Satiety and appetite can determine the quantity and quality of food consumed. Mclver et al. found in a study with 12 healthy men that hunger ratings were higher in fasted versus fed before different walking times, 15-minute walk (p 0.004), a 30-minute walk (p < 0.001), a 45-minute walk (p < 0.001), 60-minute walk (p < 0.001) and a 75-minute walk (p = 0.001); however there were no significant changes in appetite hormones . A recent study by Barutcu et al. demonstrated that morning aerobic exercise in a fasted state increases energy intake in the preceding 24 hours when compared to resting (p = 0.011) . A meta-analysis by Frampton et al. also found that subjective hunger was higher with fasted exercise in comparison to fed exercise (p < 0.001). Despite increased subjective hunger, this meta-analysis found that energy intake within the lab and energy intake (p = 0.001) and in the following 24 hours (p = 0.024) was lower in fasted exercise than fed exercise. However the same meta-analysis found that energy expenditure was lower in fasted exercise compared to fed exercise (p = 0.003), this could counterbalance the benefits of fasted exercise . This could be because the consumption of food before exercising leads to an increased thermic effect that results in greater energy expenditure than the fasted state.  The factors that cause diet-induced thermogenesis o are described in Figure 1 .
Besides fat there has to be consideration of how other tissues are affected and its effect on healthy weight loss. Fasted exercise leads to training glycogen depleted which results in double the nitrogen losses when compared to fed exercise . Training glycogen depletion which can be caused by fasted exercise is associated with the development of fatigue. This impaired performance can increase the difficulty when performing high-intensity interval training, which has been proven a superior strategy for weight loss as it has the same beneficial effect as moderate-intensity continuous training, inducing weight loss but at a shorter duration; while having a greater effect on cardiovascular disease which is beneficial for people at risk as are people with obesity [16, 17].
Weight loss and exercise in accumulated short bouts vs. continuous
In recent years discussion of which distribution of weight loss has been relevant. Heonate et al. in a meta – analysis found that short bouts of exercise consisting of less than 30 minutes and a sum of 150 weekly minutes of moderate and high intensity have a beneficial effect on reducing obesity; even do the pertains of the practice to obesity is unclear, it is believed to be easier to complete than longer exercise when there is a lack of time. Evidence suggests significant reduction on: body mass (95 % CI 0.22, 0.8), body mass index (BMI) ((95 % CI 0.27, 0.97), waist circumference (95 % CI 0.15, 0.73), fat mass (95 % CI 0.21, 0.9), body fat percentage (95 % CI 0.09, 0.58) and skinfold thickness (95 % CI 0.39, 1.53). In patients with obesity that released less than 150 minutes of exercise no significant changes were observed in the reduction of obesity indexes. BMI and waist circumference were reduced regardless of exercise duration. However, accumulated bouts of exercise greater than 10 minutes were effective in reducing body mass and fat mass and less than ten minutes was more effective when reducing skin fold .
Another meta-analysis by Murphy et al. compared the effects of continuous to accumulated exercise with the same total duration, mode, and intensity of exercise. There was a small but significant difference in the body mass changes that favor accumulated excercised compared to continuous (95 % CI -1.59, -0.25; I2 = 0%), there was also a small significant difference in fat percentage that favored accumulates in comparison to continuous exercise (95 % CI -1.71, -0.04; I2 = 0%). Additionally, there was a benefit in the reduction of LDL cholesterol with accumulated exercise versus continuous (95 % CI -0.73, -0.06; I2 = 23%) . All the studies were performed in moderate or high intensity, Table 2 describes the differences between exercise intensities.
Weight loss and exercise in the morning vs. the afternoon
The time of day people do exercise could have a beneficial factor on exercise for weight loss because of adherence, physical adaptations or the role of circadian physiology. Circadian physiology and crono – nutrition is currently being studies as a impactful intervention for weight loss. In a study by Brooker et al. that wanted to determine the feasibility and acceptability of morning versus evening exercise in overweight and obese patients found that both the gruop excersing in the morning and in the afternoon reduced body fat when doing 250 minutes of exercise no matter the time of day . To explore the effects of exercise session timing on weight loss Willis et al. conducted a 10 – month exercise program in overweight and obese, physically inactive young adults. Subjects were divided into four groups including 1) participants doing early exercise which was done in the morning, 2) Participants doing exercise between 3:00 and 7:00 pm, 3) participants doing sporadic sessions of exercise and 4) participants held as control doing no exercise. The results evidenced statistically significant greater weight loss in early exercise versus late exercise (p < 0.001), evidence also showed that a higher proportion of participants doing early exercise reached clinically significant weight loss of >5% . More recently in a study by Creasy et al. The study was done on overweight and obesity adults and lasted 15 weeks. The study group was divided into two groups: the people that exercised in the morning and the people that exercised in the afternoon. The results on weight lost were modest and similar in both groups and both groups showed adherence to exercise; results between the interventions could have been limited by the short duration of the study .
Exercise timing can have an effect on healthy weight loss if other things equal. The treatment plan for a healthy weight loss needs a healthy diet and at least 225 minutes of moderate intensity of exercise a week; establish healthy habits and then timing of exercise recommendations can be added to promote healthy weight loss. Controversy still exists in the best approach of weight loss between fasted vs fed exercise however there is evidence of a better performance in the fed state that could lead to a more effective exercise and time use. Small benefits of exercising in accumulated bouts compared to continuous exercise exist, however, the important component of exercise as a method of weight loss is to exercise at least 150 minutes a week at a moderate to high intensity. In regards to the time of exercise sessions, there is benefit from exercising in the morning for a long period of time for wanted results of weight loss. Most – information explores the timing of aerobic exercise for weight loss, further research is needed on strength exercise.
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