With intermittent fasting becoming popular amongst many people, it’s time to take a look at what the science says.
Once the preserve of religions, fasting has become the latest nutrition buzzword. You’ve probably heard of the 5:2 diet— and now there are fasting protocols like 16:8 or 18:6 popping up. Yes, there’s lots of numbers!
I am no fan of diets where food is drastically restricted to lose weight. However, no single approach suits all. Intermittent fasting offers a different way of eating that can work for some. So, with intermittent fasting supporters claiming fasting can spur weight loss, help prevent diseases and promote heart health, what does the latest science actually say?
Not what, but when
Fasting for health rather than religion started as a way to increase longevity. Enter intermittent fasting, the ‘diet’ you’re on when you’re not on a diet. That’s because rather than dictating what foods you should and shouldn’t eat, intermittent fasting determines when you should eat them and when to abstain.
Over the last 15 years, fasting research has focused mainly on what happens when food is restricted for a few days a week — intermittent fasting — rather than examining the effect of sustained periods of constant fasting. Intermittent fasting is what we will discuss here.
What does the science say?
Restricting eating to certain days or hours can deliver surprising benefits.
As well as promoting weight loss, intermittent fasting has been associated with a variety of health benefits, from improving diabetes management and reducing inflammation through to extending your life. While most human studies are still short term, current research is promising.
Fasting and weight loss
Intermittent fasting cuts your overall kilojoule intake, so you’re likely to lose weight. Intermittent fasting can help with visceral (belly) fat loss while sparing muscle mass. This is important for long-term weight management, as higher muscle mass helps to burn more kilojoules at rest.
When intermittent fasting was put up against a traditional kilojoule-controlled diet, in many cases intermittent fasting gave the same or better results, particularly in overweight and obese people.
Importantly, intermittent fasting seems to teach people that it’s okay to feel hungry sometimes. A fear of hunger can cause problems for some people who need to lose weight, and is sometimes associated with overeating. But those who try intermittent fasting say that knowing that they’ll have food at a certain time relieves this fear and anxiety.
Fasting and diabetes
There’s now increasing evidence that practising intermittent fasting may be beneficial to people who have diabetes, and that it can also be done with safety.
“Intermittent fasting may help reduce blood glucose and insulin levels,” according to accredited practicing dietitian and intermittent fasting expert, Jamie Chambers. “The most significant impact may be on people with pre-diabetes, where studies have shown that insulin resistance reduced by up to 40–45 per cent. Non-diabetic overweight adults also recorded a 20 per cent reduction in their insulin levels.”
Fasting and gut health
It seems our gut bacteria like short periods of fasting. Most of the research is animal-based, but recently a few trials with humans have shown fasting can decrease the bacteria associated with inflammation and increase bacterial diversity — two important features when improving your gut health.
Time-restricted feeding has a lot do with changes to your gut bacteria. Gut bacteria are affected by day-night body patterns (circadian rhythms). If your body has periods without food overnight, it can help re-establish disrupted circadian rhythms, improving gut health.
Fasting and brain health
Fasting also benefits your memory and mood. “Fasting can help to protect your brain from neurodegenerative diseases like Alzheimer’s and Parkinson’s disease by ‘shocking’ the brain to create new neurons,” Chambers says.
“These new neurons are more resistant to plaque accumulation, which is related to the progression of these diseases. Fasting may also make changes to the brain that improve memory and mood by stimulating the growth of new neurons and strengthening neural connections.”
Fasting and heart health
Your heart might benefit, too. “Fasting has been shown to help reduce ‘bad’ cholesterol levels and blood pressure, reducing your risk of heart disease,” says Chambers.
“Research has shown that fasting can reduce triglycerides by up to 25 per cent over 12 months. It also showed a reduction in systolic blood pressure [the pressure in your blood vessels when your heart beats] over three months.”
Is it safe for everyone?
Intermittent fasting may be beneficial for some people, but there are others who should certainly leave it in the ‘no-go’ basket. They are:
- Pregnant women
- Women who are breastfeeding
- Those with very high energy needs
- Young children
- Those with certain medical conditions. Always get advice from your doctor or diabetes team before fasting.
Be aware that prolonged fasting can sometimes lead to headaches, low energy, muscle loss and weakness.
What does an intermittent fasting day look like?
| 5:2 Full-day fast | |
| Breakfast | Small skim coffee |
| Lunch | 2 Ryvitas +95g can of tuna in olive oil (drained) +1 medium ripe tomato |
| Afternoon tea | Cup of tea + splash of milk |
| Dinner | 150g chicken breast, grilled + 2 cups mixed steamed vegetables |
| 16:8 Part-day fast | |
| Breakfast | Black coffee + water |
| Morning tea | Green tea + water |
| Break the fast at midday | |
| Lunch | Wholegrain bread sandwich with avocado, salad & smoked salmon |
| Afternoon tea | Fruit, handful of nuts + cappuccino |
| Dinner | Wholemeal pasta with bolognese sauce + parmesan + side salad with olive oil dressing |
| Supper | 170g tub of reduced-fat plain yoghurt |
| Begin fasting at 8pm |
7 tips to successful intermittent fasting
1 Be realistic
You might not want to fast on a day when you have a social event, or visitors are coming.
2 Find a routine
You don’t need to fast on the same days every week, but doing so can make it easier to get yourself into a routine.
3 Always drink enough water
Aim to drink at least 8–10 glasses every day.
4 Add lean protein…
like eggs, beans and legumes, to meals, to fill you up and help build muscle.
5 Tune into your hunger
Consider whether you’re snacking because you’re actually hungry, or because you’re bored.
6 Try not to rely on coffee
… for a quick energy hit.
7 Don’t try to overcompensate
… on non-fasting days by bingeing on high-kilojoule foods. Moderation is key!
Your fasting ‘buffet’
Intermittent fasting means there are some days or times when you get by on very few kilojoules, and other days where you eat normally.
Accredited Practising Dietitian and intermittent fasting expert, Jamie Chambers, divides such fasting into two categories:
Full-day fasting — such as the 5:2 diet — means women eat just 2000kJ (480cal) and men 2500kJ (600cal) for between one to four non-consecutive days a week — but then eat normally on the other days. (Recommended intake is8700kJ (2000cal) per day.)
Part-day fasting — known as time-restricted feeding, 16:8 or 18:6 — is conducted most days of the week and involves limiting the hours of the day in which you eat.
Generally, you eat meals over six-to-eight hours — and fast for the remaining 16–to–18 hours. Your energy intake doesn’t drastically change, but you eat all your food in a shorter time frame.
Fasting 10–12 hours overnight has been shown to improve gut health