Let’s first give a little background on intermittent fasting. Intermittent fasting describes a diet approach that has defined fasting (no food) and feasting (eating) periods. There are many popular types, like the 5:2 diet, the ADF (Alternate Day Fasting) and the 16/8 fast – to name a few. We all do our own version to a certain extent when we sleep each night.
Most use intermittent fasting to reduce their total caloric intake in the day, helping them lose weight. Others use fasting for the health benefits, but I’m not going to talk about that in this post.
Precision Nutrition has a great summary of some of the benefits (although it’s pretty long-winded), here is a summary:
Benefits:
Reduced:
- blood lipids (including decreased triglycerides and LDL cholesterol)
- blood pressure (perhaps through changes in sympathetic/parasympathetic activity)
- markers of inflammation (including CRP<, IL-6, TNF, BDNF, and more)
- oxidative stress (using markers of protein, lipid, and DNA damage)
- risk of cancer (through a host of proposed mechanisms)
Increased:
- cellular turnover and repair (called autophagocytosis)
- fat burning (increase in fatty acid oxidation later in the fast)
- growth hormone release later in the fast (hormonally mediated)
- metabolic rate later in the fast (stimulated by epinephrine and norepinephrine release)
Improved:
- appetite control (perhaps through changes in PPY and ghrelin)
- blood sugar control (by lowering blood glucose and increasing insulin sensitivity)
- cardiovascular function (by offering protection against ischemic injury to the heart)
- effectiveness of chemotherapy (by allowing for higher doses more frequently)
- neurogenesis and neuronal plasticity (by offering protection against neurotoxins)
The above is quite an extensive list of the benefits, and you might be currently thinking: so everyone should be do intermittent fasting?
Well, let’s not get excited too fast…
Some things to consider…
All of the above proposed benefits don’t have context, so let’s talk about a few things to consider:
1. Current research shows that a lot of the above benefits may only be occur after longer periods of fasting. Depending on your activity levels, this can be as much as 24 hours or as little as 16 hours – either way, it’s an extensive time window.
2. Most of the research has been done using animal models, such as rodents. This limits what we can definitively say about the impact of intermittent fasting in humans. You might be asking “why don’t they recruit people to do their studies?” The reason is that people are notoriously difficult to deal with in research, 2 big reasons: First, it would be difficult to recruit people to a study where they will starve you for a period of time, then poke you with needles, and then prod your body fat; Second, people will inherently drop out or cheat during a study, which makes them unreliable. Also, people generally will only volunteer for a study when they are given a hefty cheque which makes the cost of the study quite high.
3. Many research studies compare intermittent fasting with “normal eating”. The normal North American diet is not ideal for health, body composition or performance. This normal diet tends to be hypercaloric (high in calories) compared to the intermittent fasting diets which tend to be hypocaloric (low in calories). This tends to cause the study participants to lose weight and improve their heart health, lower their risks for diseases, improve their body composition and in general feel better. But because these studies compare to the normal diet, this does not tell us if it is the weight loss causing these improvements (which has been shown over and over again in research), or if it is specifically the fasting that is causing this. In other words, maybe we can simply restrict calories at all of our meals and snacks to experience these same benefits.
Possible Pros
Provides structure of how to eat
By following a set eating structure you’re more likely to stick to eating at set times, which will prevent you from snacking or eating more. This should help you consume less calories. If you just eat based on internal hunger signals it’s a lot harder to eat less, especially since hunger is often falsely triggered by external cues – like the smell of fresh baked goods, or wanting to snack while watching T.V.
Allowance for bigger meals
The ability to have bigger meals, which also means more calories, will allow you to feel full after each meal. One thing to note: try to enjoy your food and not “inhale” it – this can be often what happens with your first meal when you break the fast.
Flexibility
The ability to have bigger meals ties into flexibility. It allows for more flexibility in meal options, like when socializing at a restaurant where most meals are 800 calories or more. A larger caloric allowance per meal also acts as a buffer for more calorically dense foods.
Relatively simple to follow
There aren’t a lot of “rules” to follow with intermittent fasting, rather just certain eating windows. So for many, it’s a lot easier to start and continue doing.
Experience hunger
Fasting can be a good exercise to feel what it’s like to be hungry, and wait until later to satisfy it. For many, when you get hungry there tends to be this panic that sets in that you need to eat ASAP. This can sometimes cause you to grab something quick, which can often be something less nutritious. Instead, if you sit with your hunger for 10-15 minutes, the feeling tends to go away. This can be reassuring for someone, like a parent with kids who are on-the-go, who now understand that they are able to wait and eat something more nutritious later.
Possible Cons
Not enough protein?
For some it will be hard to eat enough protein in the shortened eating window (eg. it might be hard to get 100g+ of protein with just 2 meals); related read: suggested protein intake needs.
Fasted training sucks
A lot of the fasting protocols out there have you doing fasted training, or the way your exercise schedule works with the protocol you end up training fasted a lot. If you’re doing any exercise with a higher heart rate component, your training will be mentally and physically challenging.
Ignoring hunger signals
At times you’ll have to ignore hunger signals and wait until when it’s time to eat. This can be problematic later on, eating when you’re hungry and stopping when you’re full is good practice to intuitively eat to manage your weight in the future.
Intense hunger cravings
Once you initially break the fast, you’re going to get overridden with hunger signals and it’s usually hard to slow down and eat a proper serving sized meal – this includes slowing down and chewing your food properly, which has been shown to have a lot of benefits.
Fullness disinhibition
When you’re finished eating this properly portioned meal, a meal that should make you feel full, you might experience fullness disinhibition. This means that, despite eating this properly portioned meal, your brain is still sending you hunger signals – these are strong signals that are hard to ignore, similar to binge eating. Which leads me to the next point.
Disordered eating and eating disorders
Intermittent fasting can result in some disordered eating behaviors, and in some cases be the trigger for an eating disorder. “For some people who are vulnerable (genetically) to binge eating, for example, intermittent fasting can set them up for a rebound binge. For other individuals who are genetically prone to anorexia nervosa, experimenting with intermittent fasting can be the first step in a slippery slope toward anorexia nervosa,” says Dr. Cynthia Bulik, the director of the Center for Excellence for Eating Disorders at the University of North Carolina and the director of the Centre for Eating Disorders Innovation at the Karolinska Institute.
Not applicable to specific populations
In general, I’ve found fasting doesn’t always work for: those new to dieting and exercise, parents with children, and athletes – mainly because their performance and recovery will likely suffer.
You should not be doing Intermittent fasting if you have advanced diabetes, a history of eating disorders like anorexia or bulimia, are pregnant, or are breastfeeding.
Hopefully the above pros and cons give you some more insight into whether intermittent fasting is for you or not.
I’ll end with saying one thing:
Fasting is not a superior way of dieting. The best diet, both from a health or weight loss approach, is a diet that is sustainable and that works for you.
Till next time,
-Mike