Kaitlin Day, RMIT University and Sharayah Carter, RMIT University

Intermittent fasting has gained popularity in recent years as a dietary approach with potential health benefits. So you might have been surprised to see headlines last week suggesting the practice could increase a person’s risk of death from heart disease.

The news stories were based on recent research which found a link between time-restricted eating, a form of intermittent fasting, and an increased risk of death from cardiovascular disease, or heart disease.

So what can we make of these findings? And how do they measure up with what else we know about intermittent fasting and heart disease?

The study in question

The research was presented as a scientific poster at an American Heart Association conference last week. The full study hasn’t yet been published in a peer-reviewed journal.

The researchers used data from the National Health and Nutrition Examination Survey (NHANES), a long-running survey that collects information from a large number of people in the United States.

This type of research, known as observational research, involves analysing large groups of people to identify relationships between lifestyle factors and disease. The study covered a 15-year period.

It showed people who ate their meals within an eight-hour window faced a 91% increased risk of dying from heart disease compared to those spreading their meals over 12 to 16 hours. When we look more closely at the data, it suggests 7.5% of those who ate within eight hours died from heart disease during the study, compared to 3.6% of those who ate across 12 to 16 hours.

We don’t know if the authors controlled for other factors that can influence health, such as body weight, medication use or diet quality. It’s likely some of these questions will be answered once the full details of the study are published.

It’s also worth noting that participants may have eaten during a shorter window for a range of reasons – not necessarily because they were intentionally following a time-restricted diet. For example, they may have had a poor appetite due to illness, which could have also influenced the results.

Other research

Although this research may have a number of limitations, its findings aren’t entirely unique. They align with several other published studies using the NHANES data set.

For example, one study showed eating over a longer period of time reduced the risk of death from heart disease by 64% in people with heart failure.

Another study in people with diabetes showed those who ate more frequently had a lower risk of death from heart disease.

A recent study found an overnight fast shorter than ten hours and longer than 14 hours increased the risk dying from of heart disease. This suggests too short a fast could also be a problem.

But I thought intermittent fasting was healthy?

There are conflicting results about intermittent fasting in the scientific literature, partly due to the different types of intermittent fasting.

There’s time restricted eating, which limits eating to a period of time each day, and which the current study looks at. There are also different patterns of fast and feed days, such as the well-known 5:2 diet, where on fast days people generally consume about 25% of their energy needs, while on feed days there is no restriction on food intake.

Despite these different fasting patterns, systematic reviews of randomised controlled trials (RCTs) consistently demonstrate benefits for intermittent fasting in terms of weight loss and heart disease risk factors (for example, blood pressure and cholesterol levels).

RCTs indicate intermittent fasting yields comparable improvements in these areas to other dietary interventions, such as daily moderate energy restriction.

So why do we see such different results?

RCTs directly compare two conditions, such as intermittent fasting versus daily energy restriction, and control for a range of factors that could affect outcomes. So they offer insights into causal relationships we can’t get through observational studies alone.

However, they often focus on specific groups and short-term outcomes. On average, these studies follow participants for around 12 months, leaving long-term effects unknown.

While observational research provides valuable insights into population-level trends over longer periods, it relies on self-reporting and cannot demonstrate cause and effect.

Relying on people to accurately report their own eating habits is tricky, as they may have difficulty remembering what and when they ate. This is a long-standing issue in observational studies and makes relying only on these types of studies to help us understand the relationship between diet and disease challenging.

It’s likely the relationship between eating timing and health is more complex than simply eating more or less regularly. Our bodies are controlled by a group of internal clocks (our circadian rhythm), and when our behaviour doesn’t align with these clocks, such as when we eat at unusual times, our bodies can have trouble managing this.

So, is intermittent fasting safe?

There’s no simple answer to this question. RCTs have shown it appears a safe option for weight loss in the short term.

However, people in the NHANES dataset who eat within a limited period of the day appear to be at higher risk of dying from heart disease. Of course, many other factors could be causing them to eat in this way, and influence the results.

When faced with conflicting data, it’s generally agreed among scientists that RCTs provide a higher level of evidence. There are too many unknowns to accept the conclusions of an epidemiological study like this one without asking questions. Unsurprisingly, it has been subject to criticism.

That said, to gain a better understanding of the long-term safety of intermittent fasting, we need to be able follow up individuals in these RCTs over five or ten years.

In the meantime, if you’re interested in trying intermittent fasting, you should speak to a health professional first.

Kaitlin Day, Lecturer in Human Nutrition, RMIT University and Sharayah Carter, Lecturer Nutrition and Dietetics, RMIT University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Many women worry hormonal contraceptives have dangerous side-effects including increased cancer risk. But this perception is often out of proportion with the actual risks.

So, what does the research actually say about cancer risk for contraceptive users?

And is your cancer risk different if, instead of the pill, you use long-acting reversible contraceptives? These include intrauterine devices or IUDs (such as Mirena), implants under the skin (such as Implanon), and injections (such as Depo Provera).

Our new study, conducted by the University of Queensland and QIMR Berghofer Medical Research Institute and published by the Journal of the National Cancer Institute, looked at this question.

We found long-acting contraceptives seem to be as safe as the pill when it comes to cancer risk (which is good news) but not necessarily any safer than the pill.

How does the contraceptive pill affect cancer risk?

The International Agency for Research on Cancer, which compiles evidence on cancer causes, has concluded that oral contraceptives have mixed effects on cancer risk.

Using the oral contraceptive pill:

• slightly increases your risk of breast and cervical cancer in the short term, but
• substantially reduces your risk of cancers of the uterus and ovaries in the longer term.

Our earlier work showed the pill was responsible for preventing far more cancers overall than it contributed to.

In previous research we estimated that in 2010, oral contraceptive pill use prevented over 1,300 cases of endometrial and ovarian cancers in Australian women.

It also prevented almost 500 deaths from these cancers in 2013. This is a reduction of around 25% in the deaths that could have occurred that year if women hadn’t taken the pill.

In contrast, we calculated the pill may have contributed to around 15 deaths from breast cancer in 2013, which is less than 0.5% of all breast cancer deaths in that year.

What about long-acting reversible contraceptives and cancer risk?

Long-acting reversible contraceptives – which include intrauterine devices or IUDs, implants under the skin, and injections – release progesterone-like hormones.

These are very effective contraceptives that can last from a few months (injections) up to seven years (intrauterine devices).

Notably, they don’t contain the hormone oestrogen, which may be responsible for some of the side-effects of the pill (including perhaps contributing to a higher risk of breast cancer).

Use of these long-acting contraceptives has doubled over the past decade, while the use of the pill has declined. So it’s important to know whether this change could affect cancer risk for Australian women.

Our new study of more than 1 million Australian women investigated whether long-acting, reversible contraceptives affect risk of invasive cancers. We compared the results to the oral contraceptive pill.

We used de-identified health records for Australian women aged 55 and under in 2002.

Among this group, about 176,000 were diagnosed with cancer between 2004 and 2013 when the oldest women were aged 67. We compared hormonal contraceptive use among these women who got cancer to women without cancer.

We found that long-term users of all types of hormonal contraception had around a 70% lower risk of developing endometrial cancer in the years after use. In other words, the risk of developing endometrial cancer is substantially lower among women who took hormonal contraception compared to those who didn’t.

For ovarian cancer, we saw a 50% reduced risk (compared to those who took no hormonal contraception) for women who were long-term users of the hormone-containing IUD.

The risk reduction was not as marked for the implants or injections, however few long-term users of these products developed these cancers in our study.

As the risk of endometrial and ovarian cancers increases with age, it will be important to look at cancer risk in these women as they get older.

What about breast cancer risk?

Our findings suggest that the risk of breast cancer for current users of long-acting contraceptives is similar to users of the pill.

However, the contraceptive injection was only associated with an increase in breast cancer risk after five years of use and there was no longer a higher risk once women stopped using them.

Our results suggested that the risk of breast cancer also reduces after stopping use of the contraceptive implants.

We will need to follow-up the women for longer to determine whether this is also the case for the IUD.

It is worth emphasising that the breast cancer risk associated with all hormonal contraceptives is very small.

About 30 in every 100,000 women aged 20 to 39 years develop breast cancer each year, and any hormonal contraceptive use would only increase this to around 36 cases per 100,000.

What about other cancers?

Our study did not show any consistent relationships between contraceptive use and other cancers types. However, we only at looked at invasive cancers (meaning those that start at a primary site but have the potential to spread to other parts of the body).

A recent French study found that prolonged use of the contraceptive injection increased the risk of meningioma (a type of benign brain tumour).

However, meningiomas are rare, especially in young women. There are around two cases in every 100,000 in women aged 20–39, so the extra number of cases linked to contraceptive injection use was small.

The French study found the hormonal IUD did not increase meningioma risk (and they did not investigate contraceptive implants).

Benefits and side-effects

There are benefits and side-effects for all medicines, including contraceptives, but it is important to know most very serious side-effects are rare.

A conversation with your doctor about the balance of benefits and side-effects for you is always a good place to start.

Susan Jordan, Professor of Epidemiology, The University of Queensland; Karen Tuesley, Postdoctoral Research Fellow, School of Public Health, The University of Queensland, and Penny Webb, Distinguished Scientist, Gynaecological Cancers Group, QIMR Berghofer Medical Research Institute

This article is republished from The Conversation under a Creative Commons license. Read the original article.