Rapidly gaining in popularity, intermittent fasting is an eating pattern characterised by alternating windows of time for eating and fasting. Although many people may be motivated to trial intermittent fasting for weight loss, increased energy, or improved mental clarity, it may also be practised for specific health or religious reasons. However, intermittent fasting is not for everyone, and may lead to adverse health effects if not practised responsibly. Further research is also needed to properly explore its effects amongst different groups, including adult women. Before trialling intermittent fasting, it is important to be mindful of its associated risks (that we know of currently), as well as other, effective – and well-studied – dietary and lifestyle interventions that could help you achieve your goals.
Possible approaches and benefits
Although – for most of us – sleeping overnight naturally leads to a fasting window, some of the most popular, approaches to intermittent fasting include:
- The 16:8 method. Involves fasting every day for 16 hours, and restricting daily eating to an 8 hour window. This might look like having your first meal at 11am, and finishing your last meal by 7pm.
- The 14:10 method. Involves fasting every day for 14 hours, and restricting daily eating to a 10 hour window. This might look like having your first meal at 8am, and finishing your last meal by 6pm.
- The 5:2 method. Involves eating ‘normally’ for five days per week, and substantially reducing energy (calorie) intake for two, non-consecutive days per week. Fasting days are typically only 500-600 calories for the entire day.
- Alternate-day fasting. Involves eating ‘normally’ every second day, and substantially reducing energy (calorie) intake on the other days.
As intermittent fasting aims to reduce overall calorie intake and create an energy deficit, weight loss is one possible benefit. In such cases, it is especially important to maintain a nutrient-dense diet to prevent deficiencies of essential micronutrients. Other potential benefits include lowered blood pressure, improved blood cholesterol, decreased resting heart rate, and reduced inflammation. There is also emerging research that suggests intermittent fasting may be beneficial in reducing risk of Alzheimer’s disease, so may be of interest to those with a family history.
Proceed with caution
Intermittent fasting is not appropriate for:
- Children and adolescents.
- Women who are trying to conceive, pregnant or breastfeeding.
- Individuals with diabetes
- Underweight individuals.
- Individuals with a chronic illness (e.g. cancer).
- Individuals with a history of disordered eating.
- Individuals who are highly stressed.
Outside of these groups, intermittent fasting may not be suitable:
- If you have a variable schedule or routine (e.g. shift work).
- If intermittent fasting promotes a problematic or obsessive relationship with food for you.
- If you’re a very active individual, particularly if you exercise in the morning.
- Individuals with gastrointestinal conditions that experience symptoms such as nausea
- If you lose touch with your body’s natural hunger signals or find it difficult to eat mindfully when following an intermittent fasting pattern.
- If fasting causes hunger, low energy, weakness, trouble concentrating, dizziness and/or other adverse effects that don’t improve with time and/or disrupt your normal routine.
Fasting may also lead to adverse hormonal effects for women. Although research is currently limited, low blood glucose levels associated with fasting – and fasted exercise – may place stress on the body. As a result, the release of reproductive hormones may be disrupted, leading to menstrual irregularities or amenorrhea (loss of periods), which can adversely affect fertility and increase risk of endometrial cancer. It is important to note that majority of human trials for intermittent fasting have been done on men.
Intermittent fasting aside, from promoting weight loss to boosting energy and vitality, a broad spectrum of nutritional supports are available to help you meet your goals. Current research shows no significant difference in weight loss outcomes for individuals following intermittent fasting, versus other dietary and lifestyle approaches to creating an energy deficit. Moreover, although some individuals report improved energy levels, greater cognition, and enjoy the feeling of a lighter digestive load when intermittent fasting, it certainly isn’t for everyone. If you do find intermittent fasting works well with your lifestyle, it’s important to ensure you’re getting adequate nutrients in within your eating windows. Seeing an Accredited Practising Dietitian can assist with personalising this to suit you.
For expert, personalised dietary advice to support you on your health and wellness journey, book your first appointment with one of our wonderful accredited practising dietitians.
Written by Caitlin Branch, Student Nutritionist, and Amanda Smith, Accredited Practising Dietitian.
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