Intermittent fasting: a safe way to lose weight or just another fad diet?

The health benefits and risks of intermittent fasting.

intermittent fasting
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If you're hoping to lose weight, intermittent fasting might be one of the ways you're considering changing the way you eat. It is, after all, one of the most popular diets out there, and it's less about changing your food (so you can still have your favourite treats), and more about the time you eat it. But is fasting a safe diet plan and does it have any other health benefits other than weight loss?

We spoke to Dr Deborah Lee from Dr Fox Online Pharmacy and Jenna Hope, registered nutrition consultant and founder of Jenna Hope Nutrition, to get the lowdown on intermittent fasting - how it works and the advantages and disadvantages:

What is intermittent fasting?

Intermittent fasting is a type of eating pattern that differs from conventional diets as if focuses on when you can eat, rather than what you can eat. During periods of fasting, you restrict what you eat significantly.

There are several types of intermittent fasting regimes, the two main ones being:

  • The 16:8 diet: This is a daily 16-hour fast with an 8-hour eating window. 'The relatively easy way to do this is to stop eating after dinner, say at 8pm, then skip breakfast and don't each lunch until at least 12 midday the next day,' says Dr Lee.
  • The 5:2 diet: 'This is where you restrict your intake for two days a week to eating 500-600 calories,' says Hope.

    Meanwhile, you can also do a daily 20-hour fast, fasting once or twice a week for 24 hours, or even fasting every other day.

    'Water, black tea and black coffee can be drunk in the fasting window,' says Hope. 'However, caloric drinks should be avoided.'

    As for what you can eat outside of the fasting - Dr Lee says you don't need to count your calories, but to apply some common sense. 'The diet will not work if you throw caution to the wind and eat to make up for lost time!'

    'The idea is to eat nutritious, sensible meals, eat mindfully and enjoy them, but aim to eat healthily,' she says. 'Avoid processed foods as these tend to be high in saturated fat, salt, and sugar.'

    How does intermittent fasting work?

    The idea behind intermittent fasting is that it can help you lose weight, but how does it actually work? Essentially, when you follow an intermittent fasting regime, your body’s metabolism switches to burning fat to produce energy.

    Intermittent fasting focuses on when you can eat, rather than what you can eat.

    'When you stop eating, at first, your body uses all its readily available glycogen as fuel, but after 14 -16 hours, this has all been used up, and it is forced to start burning fat,' explains Dr Lee. 'This results in the production of metabolic by-products called ketones, and hence is called, being in ketosis.'

    And perhaps it's quite natural. 'When you think about it, in caveman times, our ancestors probably fasted a lot of the time,' Dr Lee adds. 'They only ate when they managed to kill an animal, or after foraging for nuts, fruits, or berries. Their bodies were used to long periods of fasting.'

    intermittent fasting
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    Intermittent fasting benefits

    So what are the advantages of intermittent fasting? Here, the experts outline several:

    ✔️ Intermittent fasting results in weight loss

    'Intermittent fasting may promote fat loss through the reduction in total energy intake and increased accessibility to fat oxidation,' says Hope.

    ✔️ Intermittent fasting can lower insulin resistance

    'One major benefit of the diet is that it lowers insulin resistance, which unchecked, can progress to full-blown diabetes,' says Dr Lee.

    ✔️ Intermittent fasting can improve cognitive functions

    'Some individuals claim fasting may help their concentration in the morning,' says Hope. Meanwhile, Dr Lee adds 'Fasting has been shown to improve cognition and prevent age-related cognitive decline.'

    ✔️ Intermittent fasting tends to lower blood pressure

    'In one 2019 study, groups of patients were observed for periods of fasting,' says Dr Lee. 'Systolic and diastolic blood pressure decreased and the fasting was also associated with a significant reduction in levels of total cholesterol.'

    Intermittent fasting side effects and risks

    Although it comes with some great health benefits, there are some downfalls to think about if you're considering intermittent fasting. Apart from feeling hungry and getting food cravings during fasting, you may also experience the following, according to Dr Lee:

    • Headaches: low blood sugars can precipitate headaches and feelings of light-headedness.
    • Gastrointestinal side effects: bloating, nausea, diarrhoea and constipation may all occur when fasting.
    • Feeling angry or irritable: when your blood sugar is low this can cause anger and irritability.
    • Fatigue: many people report feeling they have no energy when they start the fasting periods, but over time, the fasting periods can make you feel energised.
    • Dehydration: you may pass a lot of urine when you start the diet and if you can’t keep up the water intake this can lead to dehydration. Always drink plenty of water.
    • Bad breath: ketosis is associated with acetone on your breath. Coupled with dehydration, this can smell unpleasant.
    • Malnutrition: take care to eat nutritionally complete meals on days you can eat, to avoid any long term malnutrition.

      Who should avoid intermittent fasting?

      Intermittent fasting is not suitable for everyone. 'It may be a useful tool for some individuals,' says Hope. 'However, intermittent fasting is not recommended for individuals with diabetes, pregnant or lactating women and people with a history of a poor relationship with food.'

      Dr Lee adds that children shouldn't be put on this diet, either. 'Children are growing and usually have levels of physical activity, so they need a regular nutritional and calorie intake,' she says.

      ⚠️ Always consult your doctor before starting a new diet plan.

      Last updated: 21-06-2021

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