Losing Weight through Intermittent Fasting

In my last post which looked at my recent (and continuing) weight loss success, I promised to talk about how I had changed my diet to achieve this level of weight loss.

What I have been doing is a form of 'intermittent fasting' based on the book "Eat Stop Eat" by Brad Pilon.

Without going into the whole whys, wherefores, reasons and whatever around intermittent fasting, what it basically means is not eating for around 24 hours at time - and Brad recommends doing this 1 or 2 times per week.

Before I got the book, I had a handful of major questions, some of which were answered by the book, and others through my experience of sticking to the plan (which I have done now for just over 3 weeks).

Question 1) Would I lose weight - what about starvation mode?

Well I think that my weight loss results , so far, speak for themselves. I'm still continuing to lose weight although at a slightly slower pace than at the start. Initially, I was losing around 2kg per week, but this week it's more like 1.5kg. Not sure if this is a blip or not - we'll see over the next few weeks I guess.

I don't have body fat scales at home, so I can't tell you anything statistically about body composition, other than I look much flatter in the mirror.

In terms of 'starvation mode' then I looked up a few of the studies which Brad researched. There is a key study which looks at the impact of intermittent fasting on metabolic rate, lean body weight, body fat etc. The study (and Brad) point to the fact that the base metabolic rate of the subjects is roughly the same on fasting and non-fasting days to say that there is no drop in metabolic rate from intermittent fasting.

However, when you compare the metabolic rate 21 days after starting intermittent fasting, to the day before starting intermittent fasting, there is roughly a 10% drop. Before everyone screams "starvation mode!" let's compare that to the fact that these subjects are now ingesting almost 50% fewer calories. Therefore, the calorie reduction massively outweighs (no pun intended) the slight reduction in metabolic rate.

Furthermore, between 80% and 90% of the weight loss was in the form of pure fat, with the rest being made up of muscle. Again that gives ammunition to the 'starvation mode' camp - the fact that they lost muscle mass - but the vast majority of weight loss was in fat. Additionally, it is apparently normal for 'fatter' people to have more muscle mass than lean people anyway - we need it to haul our fat butts around! So when we lose weight, it only makes sense that we need less muscle...

Question 2) Would I feel sluggish the way I sometimes do if I get hungry?

From my experience so far, absolutely not. In fact, there is some research to suggest that metabolic rate actually increases slightly in the first 24 hours of a fast. Some have postulated that this is a sensible evolutionary trait - when our ancestors got hungry, they would need to be more alert and energetic so they could go out and hunt food. This makes sense to me (although I'm no dietician...).

Question 3) Would I feel hungry when fasting?

The biggest surprise to me is that I don't feel hungry when fasting. Well perhaps just a little bit but no more than usual. I used to hit 12 o'clock and immediately race out to get some food. Sometimes earlier. Now that I'm fasting, I realise that that urge to eat was not a need to eat - it was purely a learned pattern of behaviour that I'd need to unlearn. Just as someone may feel that they need a drink when they get home from work. They don't need that drink (unless they have alcohol dependency issues) - it's just a learned pattern of behaviour.

So when 12 o'clock comes around, rather than going to get food, I instead go to the coffee machine and get myself some green and peppermint tea which seems to satisfy my urge to put something in my mouth.

(By the way, I hate the taste of green tea but I hear that it's very good for you. So what I do is to put a green tea bag and a peppermint tea bag into the same cup so I get the benefits of the green tea but the taste of the peppermint tea. I've now noticed a number of my colleagues do the same now that they've seen my trick!)

Question 4) Is intermittent fasting healthy?

Well, as far as I'm aware no-one has proven that intermittent fasting is unhealthy. People have been able to prove that prolonged fasting or severe calorie restriction have depressed metabolic rate (although never enough to cancel out the impact of reduced energy intake on fat stores) and have reduced muscle mass (albeit with between 5 to 10 times as much fat being lost). I'm happy to take these two impacts along with the benefits of fat loss.

In addition, however, Brad'd book puts forward a bunch of different health benefits from intermittent fasting, including increased insulin sensitivity. In fact, it was this alone which made me look at the book in the first place. As an overweight (previously obese) person, I was at high risk of contracting diabetes and I wanted to make sure I didn't get there - hence trying to reduce insulin resistance.

Two of the other key benefits I have seen however as as follows:

Firstly, I just have much more time in the day. I no longer spend 10 minutes in the morning eating breakfast and tidying away. I no longer spend 20-30 minutes getting and eating lunch - instead I can work straight through and stay massively focused on what I'm doing.

Secondly, I have a completely different relationship with food. When I look at food now, I'm no longer eating because I feel massively hungry and just have to get food into my stomach. I'm far more balanced, and can make much more sensible food choices. I now ask myself what the food can give me, rather than just grabbing whatever is available. I actively choose salads and vegetables in restaurants now - not because I want to 'be good', but because I know that I want to get a bunch of vitamins and minerals into me.

Question 5) Would I be able to work out while fasting?

Apparently, adrenaline levels are slightly increased in the first 24 hour of a fast - for the same reason that metabolic rate increases. Which should mean that workouts should be just as effective (if not more so) when fasting.

However, I'm not quite sure how this works. Presumably in a fast, all of the muscle glycogen gets used up (that's why fat is being burned). But that means that when you work out, there is no muscle glycogen left meaning you need to burn fat instead, which is (as far as I understand) much slower to release energy. I'm going to ask Brad about this and see what he says.

My workouts have felt just as intense as before I started intermittent fasting - however I was not working out consistently before I started, so I don't have a quantified benchmark with which to compare my strength. What I am able to say, however, is that my strength has definitely increased WHILE I've been doing intermittent fasting. Not massively (I was always quite strong anyway) but it's definitely noticeable.

The thing which I find most puzzling at the moment is my 5k time, which has stuck at between 29:30 and 30:00 despite losing 6kg.

There are, potentially, a couple of explanations I can think of.

Firstly, perhaps the reduction in muscle mass is greater than I thought and I'm too weak to take advantage of the weight loss to run faster.

Secondly, perhaps the intermittent fasting means that I don't have enough glycogen in my muscles at the time I do my run to ensure a good performance.

Thirdly, perhaps it's just the impact of a substantial increase in training volume (mentioned in my last post) which means that my muscles are more fatigued than they used to be, masking any underlying fitness gains.

Fourthly, perhaps it's my running technique and that, whatever weight/strength/fitness I am, I won't be able to run more quickly with poor technique.

Right now, I'm thinking it's probably a combination of the second and third reasons. If I'm right, that should mean that I will start seeing gains in my 5k time soon, as the weight continues to drop off (as I won't be MORE glycogen depleted, or MORE fatigued than I am now). If I'm wrong, I'll look at getting my technique looked at.

Wrap up on intermittent fasting

So, there you have it - my experiences of intermittent fasting with Eat Stop Eat. If you're interested in more of the science behind the approach, as well as how to apply it, I'd recommend picking up a copy of the Eat Stop Eat book by clicking on the link.