What is Intermittent Fasting?
Intermittent Fasting is a lifestyle in which you eat only during certain times of the day or certain days of the week.
What are the Different Types of Intermittent Fasting?
Daily Fasting/Time Restricted Feeding
In these fasts, you fast every day and divide the 24-hour day into feeding and fasting windows, here are some popular versions, but you could choose any ratio of 24 hours with the goal being to shorten your feeding window and lengthen your fasting window from your typical. They are usually written as fasting hours:feeding hours e.g. 14:10.
The main advantage of a 12:12 is that it will help you to reduce snacking in the evenings after dinner.
For this one, you could still consume three meals a day. You could use meal timing such as 10:00 breakfast, 2:00 pm lunch, 5:30 pm dinner. You should be finished eating your dinner by 6:00 pm so that all of your eating is done within 10 am until 6 pm which is eight hours.
With 20 hours of fasting and four hours of eating, you won’t be eating three meals, you’ll feel most comfortable with two meals or one meal and a snack. It will be easier to gradually work up to this much fasting.
One Meal a Day “OMAD” is described as a 23:1 but many people call their eating style OMAD, which means they only eat one meal a day, but don’t confine themselves to only one hour eating window. However, if you want to try OMAD, you should work up to this one and not start with it.
As I mentioned, these are just some of the popular fasting/feeding windows, you don’t need to restrict yourself to these and you don’t need to only do one. For example, you might do a 18:6 from Monday-Thursday and 14:10 on Friday-Saturday. You may especially want to incorporate some flexibility once you reach your goal weight and are doing maintenance. If you are still losing weight, you may prefer to keep a shorter eating window.
Weekly Fasting Regimes
These are based on the number of feeding and fasting days in a week. For these, they are expressed opposite to time restricted feeding, where the days you eat are listed for for example, eating 4 days:fasting 3 days would be 4:3.
For this one, you eat normally five days a week and fast for two days. The research has used both consecutive and non-consecutive days for the fasting. Typically these are not complete fats i.e.water only, but they are low calorie days and you would consume about 25% of your calorie needs, usually around 500-750 calories per day and are often called “modified fasts”.
This is alternate daily fasting. As the name implies, you eat your regular meals one day and fast the next day. This is usually a water only fast, but can also be a low calorie/modified fast. If you think of it in terms of time restricted feeding it is 36:12 in which you stop eating after dinner on day one for example 7:00 pm, then fast all of day two and break your fast on day three with breakfast at 7:00 am. This would add up to 36 hours of fasting and 12 hours of eating or 36:12.
When you fast more than 48 hours consecutively, that is considered an extended fast. This is also called a prolonged fast. Your ghrelin (hunger hormone) peaks at about 18 hours, so you can find yourself wanting to give in. If you are able to get past this, most people report that day three and beyond is easy. To minimize hunger, you can time your fast so that your gherlin peaks while you are sleeping. The extended fasts should be done with medical supervision.
Why Do Intermittent Fasting?
Intermittent fasting is primarily done for weight loss, but it has metabolic benefits as well. I’ll outline what research has shown for intermittent fasting for women over 40, and what women over 40 could expect from intermittent fasting.
Benefits of Intermittent Fasting Include:
I’ll review the research around each of these. I’ll focus on human research, if I do share animal research, I’ll be sure and tell you it’s animal research (this is one of my pet peeve’s! ‘Health professionals’ talking about research shows xyz and when I look it up, it’s an animal study. I won’t do that to you!)
Eight women and 8 men, non-obese (BMI<30) did three weeks of alternate daily fasting (ADF). But were instructed to eat double their food on the feeding days (this is not what is done in practice). Weight was lost despite being told to eat twice the food.
An interesting finding in this study is that the women, had higher levels of ghrelin. Ghrelin is the ‘hunger hormone’ and is responsible for making you hungry. The researchers speculated that the women’s ghelin levels may be related to carrying fat around the middle (Helbronn, 2005 AJCN).
Weight loss has been shown to be similar for alternate daily fasting and the traditional way of losing weight called continuous calorie restriction (Catenacci, 2016)
In an interesting study of women over 50. They were put on one of three diets:
- A Mediterranean style diet with 70% of their estimated calorie needs
- Alternate day fasting with 100% of their estimated calorie needs
- Alternate day fasting with 70% of their estimated calorie needs
They lost the most weight and body fat with the alternate day fasting with 70% of their calorie needs, meaning that ADF was better than traditional low calorie eating, which also restricted calories to 70%. In fact eating 100% of their calorie needs still allowed the women to lose 6 lbs of weight and 5 lbs of fat in 8 weeks (Hutchinson, 2019).
When comparing two months of ADF with continuous calorie restriction, with men and women, lost similar amounts of weight. But in five months of weight maintenance, those on ADF regained more lean mass and lost fat while the continuous calorie group regained some fat and some muscle but less than the ADF group (Catenacci, 2016).
In a study of overweight women between the ages of 20 and 69, researchers randomly divided the women into one of three different diets for three months;
- Daily calorie restriction (25% fewer calories than they required)
- Intermittent fasting 5:2 with low carb (<40 grams per day)
- Intermittent fasting 5:2 with low carb (<40 grams per day) as much protein and fat as they wanted
The calories were estimated based on the women’s basal metabolic rate and subtracting 25%. The diets were all in the range of 1200-1800 calories per day. The 5:2 diet restricted food on two consecutive days and the women ate about 600-650 calories with a maximum of 40 g of carbohydrate as this was a modified fast protocol and not a water fast.
The third group ate the same baseline diet but were allowed to have unlimited protein (meat, fish, eggs, tofu) and vegetable oils. After three months, they were all told to follow a Mediterranean diet that would meet 100% of their estimated calorie needs (the IF groups switched to 6:1). The results were as follows;
- Intermittent fasting 5:2 low carb group: significantly greater reductions in insulin and insulin resistance compared with daily low calorie group. This group had the most people that lost at least 5% of their body weight.
- Intermittent fasting 5:2 low carb group plus protein and fat: reduced insulin and insulin resistance about the same as the daily low calorie group. This group had the smallest percentage of weight loss that came from fat, which makes sense as protein will stop ketosis (fat burning).
In addition, all groups reduced inflammation, cholesterol levels and blood pressure. Both of the intermittent fasting groups lost more body fat than the daily calorie restriction group. In conclusion, the authors report that the IF 5:2 diet with less than 40 grams of carbohydrate per day gave the best results of the three diets for loss of body fat and improving insulin sensitivity (Harvie, 2013).
Improved Insulin Resistance
A study of women aged 30-45 years, who had gained at least 10 kg since age 20, over half of whom had a history of breast cancer was conducted (Harvie, 2011). The women followed either a low calorie diet or a 5:2 intermittent fasting with consecutive fasting days. The menu for the fasting day was 1.1 L of semi-skimmed milk, four portions of vegetables, one portion of fruit and a salty low calorie drink.
All the women experienced improvements in insulin levels and insulin resistance, but the 5:2 IF fasting group had greater improvements (Harvie, 2011). The same was seen by this same author in a study two years later (which I describe above) with women (aged 20-69) who reduced their insulin and insulin resistance in the 5:2 IF group versus low calorie diet (Harvie, 2013).
Improved Blood Sugars
In an Australian study, 77 women (and 60 men) with a mean age of 61 were randomly assigned to either a continuous calorie restriction or 5:2 intermittent fasting with a minimum of 50 grams of protein and 500-600 calories on two non-consecutive fasting days. After 6 months, both groups had successfully reduced their HbA1C (hemoglobin A1C) levels. In addition, the women were able to reduce their diabetes medication. But the amount of insulin needed was reduced more in the 5:2 intermittent fasting group compared to the continuous calorie restriction group (Carter, 2018). If you are taking sulfonyureas or insulin to manage your diabetes, be sure to work with your physician or registered dietitian to prevent low blood sugars while doing intermittent fasting.
The women in the study described above were able to achieve a reduction in inflammation (hsCRP) and oxidative stress, which is especially important given the large number of women with breast cancer family history. Neither group had a significant rise in ghrelin, the hunger hormone (Harvie, 2011).
One problem that can happen with weight loss is a reduction in the resting metabolic rate or the ‘metabolism’. When this happens, it makes weight regain easier, as the body isn’t burning as many calories. In a study comparing eight weeks of ADF with continuous calorie restriction, the metabolism was maintained in ADF but it went down in continuous calorie restriction. This study was mostly women with 9 and 10 women aged 39-42 in each group (three men with in each group too) (Catenacci, 2016). This is a very promising result for women over 40 that want to try intermittent fasting.
Reduced Blood Lipids and Blood Pressure
The trial of women described above also experienced improved total and LDL cholesterol and triglycerides as well as blood pressure. Both the women doing the 5:2 intermittent fasting and the women in the continuous calorie restricted experienced the same benefits (Harvie, 2011).
Women versus Men
Both men and women experienced a significant reduction in insulin, ketones (beta-hydroxy butyrate) and free fatty acids on alternate day fasting, suggesting that women as well as men can benefit. The women did have higher levels of hunger hormones though. (Halbronn, 20015 AJCL), but this result is not seen in all studies.
In a separate publication on the same group of fasters, women were not as efficient at clearning glucose after a meal following three weeks of alternate day fasting. Of note, this change was only noted for women, the men had no change in their glucose clearance. What could this mean for women? It’s hard to generalize these results as the participants were told they could eat double their food intake on their eating days (Heilbronn, 2005 ObesRes) which is not typical.
Should Women Over 40 Do Intermittent Fasting?
I think intermittent fasting is a safe option for women over 40. There have been several studies that have included women over 40 that show these diets are a good option. I suggest you work with a registered dietitian, especially if you have type 2 diabetes, or other health conditions that requires a therapeutic diet. IF provides an alternative strategy to the traditional approach to continuous calorie restriction and for many people is a more sustainable approach.
Intermittent Fasting for Women Over 50
This is the age at which women are generally premenopausal, the average age of menopause being 52. This is generally accompanied by a shift in body fat from the hips and thighs to the lower abdomen. With lower levels of estrogen, women also lose their protection against heart disease and osteoporosis. Intermittent fasting can help with menopausal weight and fat gain and help to reduce blood cholesterol, blood pressure, insulin resistance and improve sleep. While this cohort haven’t been specifically studied, many of the studied mentioned above included women over 50 in their research.
Other Forms of Fasting
When we think of fasting, we think of not eating, but the ketogenic diet and methionine restricted diets could also be considered a form of fasting. If you would like to read more about these, then check out my other Cancer Bites blog posts
Fasting for Cancer and Lymphedema
I believe Intermittent Fasting is helpful for Lymphedema too. To read more about diet for lymphedema check out my blog post Lymphedema Diet
I explores the topic of Starving Cancer, in which I explain the three different methods to achieve this. Read about them, in my blog post Starving Cancer
References for Intermittent Fasting for Women Over 40
Carter S, Clifton PM, Keogh JB. Effect of Intermittent Compared With Continuous Energy Restricted Diet on Glycemic Control in Patients With Type 2 Diabetes: A Randomized Noninferiority Trial. JAMA Netw Open. 2018;1(3):e180756. Published 2018 Jul 6. doi:10.1001/jamanetworkopen.2018.0756
Catenacci VA, Pan Z, Ostendorf D, et al. A randomized pilot study comparing zero-calorie alternate-day fasting to daily caloric restriction in adults with obesity. Obesity (Silver Spring). 2016;24(9):1874-1883. doi:10.1002/oby.21581
Harvie MN, Pegington M, Mattson MP, et al. The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. Int J Obes (Lond). 2011;35(5):714-727. doi:10.1038/ijo.2010.171