Fasting has been practiced for thousands of years in various religions during specified fasting seasons and as part of celebrations. However, intermittent fasting for weight loss and general wellbeing is growing in popularity. Just how beneficial is intermittent fasting for your health, and what’s the impact of the time of day you eat? Dr Ranil de Silva, consultant interventional cardiologist, explores more about how different types of intermittent fasting diets can impact your cardiovascular health. 

What is intermittent fasting? 

Your diet is closely linked with your heart health. A healthy, balanced diet is widely known to reduce your risk of developing coronary heart disease and diabetes, as well as helping to manage your weight and lower blood pressure.  

There is increasing evidence that the time that you eat may also affect your heart health, with intermittent fasting increasing in popularity. 

Intermittent fasting is based on the principle of eating only during specified hours and fasting for the remaining hours in between. There are different types of intermittent fasting, each with varying eating windows. Examples of popular intermittent fasting diets include: 

  • 16:8 diet 
  • 5:2 method 
  • alternate day fasting 
  • 24 hour weekly fast 

“Each of these diets may suit different people, accounting for varying health and lifestyle factors,” says Dr de Silva. “Understanding what each of them involves, and how they have been shown to affect your cardiovascular health, can help you to make an informed decision about the benefits of taking up intermittent fasting.” 

The 16:8 diet and its benefits

The most common type of intermittent fasting is the 16:8 diet, which involves fasting for 16 hours and eating a normal diet for the remaining 8 hours. “You can choose your 8 hour eating window to fit with your own lifestyle and work commitments, for example from 10am to 6pm or 12pm to 8pm,” explains Dr de Silva. “The 16:8 diet typically means cutting out one meal per day which, for many 16:8 participants, tends to be breakfast.” 

However, observational studies have shown that missing breakfast regularly is connected to a higher risk of obesity. Being obese also brings negative impacts on cardiovascular health, including increasing your likelihood of developing diabetes and high blood pressure – both of which can in turn increase your risk of developing cardiovascular disease. 

But could these findings simply be due to other lifestyle factors associated with those who regularly miss breakfast? Randomised control trials, where participants are instructed whether to eat breakfast or not, haven’t generated these same results, suggesting that more research in the area is required. 

Contrastingly, a study investigating the effects of the 16:8 diet in mice demonstrated that an eating window of 8 hours reduced their risk of obesity, inflammation and diabetes. These findings were consistent, even when the total number of calories consumed was the same as mice that ate at whichever time they chose to. The authors of the study suggest that, based on these results, intermittent fasting may be “an intervention in humans that could prevent obesity and its associated metabolic disorders.” 

Other potential benefits of the 16:8 diet are said to include improved blood sugar control (due to decreased fasting insulin and blood sugar levels), possibly reducing your risk of developing diabetes. 

Blood sugar levels in people with diabetes can be checked by a finger prick test

Blood sugar levels in people with diabetes can be checked by a finger prick test

What is the 5:2 intermittent fasting method? 

The 5:2 method is so named as it involves following a standard, non-restrictive diet for 5 days of the week, and then consuming a smaller number of calories on the remaining 2 days (typically in the region of 500-600 calories). The 2 fasting days should be broken up by a normal day of eating in between to ensure that you have sufficient caloric intake. 

The British Heart Foundation notes that “some studies have linked [the 5:2] diet to lower rates of coronary heart disease,” but acknowledges that more research is needed to produce statistically significant results. They also acknowledge that it is not yet known whether the 5:2 diet can be maintained in the long-term. 

A randomised trial which looked at 107 overweight women found that there was no difference between restricting calories every day, and following the 5:2 diet, in terms of overall weight loss – the overall weight loss was similar across the two groups.  

The study also showed that following the 5:2 method leads to reduced insulin levels, a factor which lowers your risk of developing diabetes. Over an extended period, high blood sugar levels in diabetic people can damage the heart’s blood vessels, and lead to the development of fatty deposits, blocking blood flow to the heart, and potentially leading to a heart attack. 

“However, this study was small and did not show statistically significant differences, but given the close link between diabetes and heart disease, it does indicate that the 5:2 diet may have positive effects on your cardiovascular health,” says Dr de Silva. 

What are ‘alternate day’ and 24 hour weekly fasts? 

Alternate day fasting takes the principles of the 5:2 diet but applies them to 3 or 4 days in the week, rather than just 2 days. Alternate day fasting typically involves avoiding solid foods on fasting days, or eating only up to 500 calories, while following a normal, healthy diet on the other alternate days. 

This method effectively means that people consume around 4,500 fewer calories on a weekly basis (based on an average intake of 2,000 calories on a normal day), with research showing that alternate day fasting results in an average of 5.2kg lost over 12 weeks. 

The study also looked at whether the risk of coronary heart disease in participants was lower, and found that alternate day fasting and its associated weight loss decreases bad cholesterol, alongside inducing positive changes to blood pressure. High blood cholesterol is a risk factor for heart disease, so lowering this with your diet is overall positive for your cardiovascular health. 

The 24 hour weekly fasting method is exactly as its name describes – you consume no food for a day each week, drinking only water or tea/coffee without milk during this period. Simply put, this diet means that your weekly caloric intake is around 2,000 calories lower than if you followed standard dietary guidelines every day of the week.  

The main benefits of this type of fasting are weight loss and potential favourable alteration of the gut microbiome which is associated with reduced cardiovascular risk. 

Read more about coronary heart disease, its symptoms, and how it can be diagnosed and treated. Discover how lifestyle changes – including dietary changes – can help to reduce the build-up of fatty deposits in the arteries. 

Losing weight can help with lowering the risk of diabetes and coronary artery disease

Is fasting good for your health?

Mostly, clinical trials have failed to demonstrate significant improvements with intermittent fasting over general caloric restriction. A 2017 study of obese people who adopted intermittent fasting for a year lost slightly more weight than other participants, but this was not statistically significant and therefore requires further research to prove its effectiveness. 

That said, reducing overall caloric intake – especially if you are overweight – has a positive impact on weight loss and your heart health. Intermittent fasting is just another form of restricting calories, but doing so in regular concentrated periods, rather than spreading the calorie deficit evenly across all days. 

“It’s possible that restricting yourself to a small eating window may mean you have less energy across the entire day, affecting your ability to exercise and feel well-nourished,” explains Dr de Silva. “Striking a balance is key. While weight loss, blood sugar control, and reducing coronary artery disease are undoubtedly potentially beneficial effects of fasting, a potentially reduced ability to exercise is not.” 

Is fasting right for you? 

Fasting is not suitable for everyone. It’s generally advised that you check with your doctor before adopting a fasting diet. This is especially true for people who: 

  • are pregnant or breastfeeding 
  • have type 1 diabetes 
  • have or previously had eating disorders 
  • are aged under 18 

Experiencing symptoms such as headaches, sickness, fatigue, or extreme hunger might suggest that intermittent fasting isn’t right for you, and that your body requires more regular caloric intake. 

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