Intermittent fasting, in which you restrict your energy intake on certain days, can lower you blood pressure. A study published in the British Journal of Nutrition found that following the 5-2 intermittent fasting diet led to a greater fall in systolic blood pressure than a normal calorie controlled diet.
Intermittent fasting results
Researchers from the University of Surrey asked overweight volunteers with central obesity (waist circumference greater than 94cm for men, or greater than 80cm for women) to follow either the 5-2 intermittent fasting diet or a daily calorie restricted diet with the aim of losing five per cent of their weight (eg 4kg for someone who weighs 80kg, 5kg for someone weighing 100kg).
Those following the 5-2 diet ate normally for five days of the week (self-selecting food to provide their estimated daily energy needs) while on their two consecutive fasting days they consumed just 600 calories per day (using Lighter Life Fast Foodpacks).
Those on the energy restricted diet were asked to eat 600 calories fewer per day than their estimated requirements, so the women ate around 1400 calories per day, while the men ate around 1900 calories a day.
Overall, those following the intermittent fasting diet ate 22% fewer calories than needed to maintain their weight, while those following the calorie controlled diet ate 23% fewer calories than their estimated needs.
With expert guidance to help keep them on tract, those following the 5-2 diet achieved their 5% weight loss in 59 days, while those on the calorie controlled diet took two weeks longer to achieve their goal at 73 days. However, only 27 of the 41 who originally started the diets completed the study – around one in five from both groups dropped out because they struggled to follow the diets properly, or became demoralised by not losing weight at an acceptable rate.
5-2 diet and blood pressure
The participants following the intermittent fasting diet had a greater reduction in systolic blood pressure (the upper figure) than those following the calorie controlled diet. Systolic blood pressure reduced by 9% on the 5-2 diet, compared to a small 2% increase on the daily diet.
At the start of the study, approximately half of those randomised to follow the intermittent fasting diet either had prehypertension (120–139/80–89 mmHg) or hypertension (greater than 140–159/90–99 mmHg). Following weight loss, all but one came down into the normal, healthy blood pressure range of less than 120/80 mmHg. Across the group, average blood pressure dropped from 123/74mmHg to 111/69mmHg – a reduction of 12/5 mmHg. This significant reduction in systolic blood pressure would reduce the long-term risk of a heart attack or stroke if sustained.
In those randomised to follow the calorie controlled diet, the proportion who had prehypertension or hypertension (approximately 30%) did not change significantly, despite weight loss. However, their initial average blood pressure was less than for the other group at 115/75 mmHg and reduced slightly to 111/70 mmHg – a reduction of 4/5 mmHg.
5-2 diet and triglycerides
In those following the 5-2 diet, blood levels of triglyceride fat also cleared more quickly after eating than in those on the daily calorie controlled diet.
What is intermittent fasting?
Intermittent Fasting became a popular diet trend following the BBC Horizon documentary Eat, Fast, Live Longer in which Dr Michael Mosley lost almost a stone (14lbs) in weight and 25% of his body fat over just five weeks.
Essentially, intermittent fasting means following alternating periods of eating and not eating, so you only consume food during certain feeding windows. The length of each fasting and feasting period depends on which type of diet you follow.
In fact, most of us fast for at least 8 hours a day, during our sleeping period, so intermittent fasting is just an extension of this natural food break. The downfall of intermittent fasting is that it’s easy to binge on your free eating days and to make unhealthy choices.
Although intermittent fasting may sound easy, there are lots of decisions to make: How often should you fast? For how long? Should you eat zero calories on fasting days, or enjoy at least some food? Should you eat the same amount of food on non-fasting days as normal, or eat less or even more?
Typically, on a fasting day you restrict your calorie intake to about one-quarter of your recommended daily intake so you still obtain some nutrition and, most importantly, fluids. However, some people prefer to have fluids only (eg soups, juices) on a fast day, with no solids, while others have nothing but water.
Intermittent fasting diet plans
The most popular intermittent feasting and fasting regimes are as follows:
5-2 Diet – 2 days fasting, 5 days normal eating
This is the easiest and most popular plan as you fast on any 2 days of the week you choose, eating no more than 500 or 600 calories. The remaining days you eat whatever you want. In the study described above, the 2 fasting days were consecutive, but this is not usually obligatory. Fasters are encouraged to make good eating choices, but there are no firm restrictions on your non-fasting days.
Eat Stop Eat – 24 hour fast, once or twice a week
In this plan, you fast for a full 24 hours, once or twice a week while eating sensibly for the rest of the week, selecting foods that are high in protein, and avoiding processed foods. It’s flexible in that you can choose on which days you fast, and you can choose to fast from breakfast to breakfast, or from dinner to dinner.
The Warrior Diet – fast for 20 hours, eat during a 4 hour period
The Warrior Diet revolves around either fasting, or eating small amounts of specifically recommended foods, for the first 18 to 20 hours of each day, and exercise during this period of under-eating. There is evidence that moderate exercising while fasting helps the body burn more fat. You then eat the majority of your daily food intake within a small 4 to 6 hour window, then repeat the cycle. Most people position their feeding window towards the end of the day so they can exercise after work, then enjoy a family dinner.
Alternate Day Diet – eat normally one day, fluid fast the next
In this regime, you eat normally on alternate days, and fast in between.
The 16-8 or Eight Hour Diet – fasting for 16 hours and eating during an 8 hour window
In the 16-8 plan, you only eat during an 8 hour window, most often from 12 noon until 8pm at night. This most closely follows the normal eating pattern for many people, such as those who tend to skip breakfast.
How intermittent fasting works
Intermittent fasting usually (but not always) means you eat fewer calories overall. After the initial period in which you feel hungry, your metabolism adapts and most people report feeling less hungry overall and, when they do eat, they feel full more quickly.
When food intake is restricted, your body is forced to find energy elsewhere by mobilising glycogen ( a starchy energy store laid down in liver and muscle cells) and fat (from adipose tissue stored around your internal organs and under the skin). Intermittent fasting is also believed to promote cellular repair, as cells also breakdown their own damaged proteins for energy and then replaces what it has consumed when you next eat. This recycling process is said to both slow the ageing process and prevent disease. With prolonged fasting, however, the body would also break down healthy muscle protein for energy, but this is largely prevented by having regular feeding windows.
Intermittent fasting also improves insulin sensitivity, has beneficial effects on growth hormone secretion (to promote fat loss and muscle gain), suppresses inflammation and boosts immune responses.
Intermittent fasting requires commitment and motivation. It isn’t for everyone, you may find it helps you to lose weight if nothing else has worked, as well as improving your blood pressure control.
If you decide to cut back on food intake to lose weight, I strongly recommend that you take a good quality vitamin and mineral supplement to avoid micronutrient deficiencies.
NB If you plan to fast for more than one or two days, always seek medical advice first.
If your blood pressure is raised, self-monitoring is key to maintaining good control.
Click here for advice on choosing a blood pressure monitor to use at home.
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