Eating for a Marathon: Weight Loss

Last week I talked about some of the techniques I used to encourage my body to use fats as fuel. Most people assume that burning more fat during exercise will result in weight loss.  Sadly, this is not true. To lose weight, you need a calorie deficit – to be taking in less energy than you use. No calorie deficit, no weight loss, as I experienced first hand.

Like most people, I put on a few pounds over Christmas, and on 1 January 2020 I weighed in at 65.7Kg and 30% body fat. I had lost some body fat in January and early February, but I then went to Canada for a couple of weeks for a wedding. When I got back, I weighed 65.4 Kg and 29% body fat – basically back to where I was in early January. As I got back into training, I was hoping the healthier eating and increased running would lead to fat loss.

By the first of April I was down to 64Kg. However, despite an ever increasing training regime, I stayed at 64Kg and 29% body fat. Health and aesthetic benefits aside, I had another reason for wanting to shed some weight. Studies have shown that runners are, on average, two seconds per mile faster for every pound they lose. If I lost 5lbs of fat, I should be a good 4 minutes faster over the course of a marathon.

So I decided to switch up my training and nutrition for a couple of weeks to encourage weight loss. Up to that point, I’d been eating a base of around 1800Kcal per day, then adding exercise calories on top. For example, if I burned 400Kcal on a run, I ate 2200kcal that day. From the 18th of May, I switched to a 1500kcal base. I was still adding the exercise on top, so in reality I was often getting 2000kcal per day.

To ensure I was losing fat and not muscle, I increased by protein intake – at least 1.8g/Kg per day. I did keep carbohydrates in my diet, but was much more strategic in when I had them. I tried to have higher carbohydrate meals after exercise, and lower carbohydrate meals at other times. I also kept an eye on the amount of fat in my diet, to keep the calorie count down. But it wasn’t exactly a low fat diet either. Of course, there was no alcohol and very few refined sugars (the kind you find in chocolate, cake, etc.).

I also switched up my training to further encourage fat burning. On Mondays, Wednesdays and Fridays I went for a 45 minute walk before breakfast, while on Tuesdays and Thursdays, I did an hour long fasted run. I kept my hill sprints on Monday afternoons, and my long run on Saturdays. I was up to an hour and a half on the long run, so I did have breakfast before, but I didn’t take on any carbs during the run. There were also a couple of HIIT/strength training sessions per week (as normal) and I made an effort to get 10,000 steps a day, most days of the week.

And it worked. On June first I weighed in at 61.8Kg and 26.3% body fat. In two weeks I had lost over 2kg and most of that was body fat, not muscle. However, it was not easy. I was often tired and hungry, despite a high protein and high fibre diet. And the quality of my hill reps and HIIT sessions really suffered – I just didn’t have the energy to push myself.

In some ways losing weight to get faster is a short cut. In two weeks I lost enough weight to take 4 minutes off my marathon time. It could take months to get that much from training. And it can be tempting to keep going, especially when you know you have plenty of body fat to lose (26% body fat is high for a runner). But it is a game that catches up with you in the end – as I discovered, your training really suffers.  I decided that I would get better results by hitting all my training targets, rather than chasing a lower body weight.

The good news is that on September second I was still 61.8 kg –  no more, no less. All while fuelling ever increasing amounts of training!

Please note: This is a description of my personal experience of losing body fat to meet a specific performance goal. It is not meant to be taken as a recommendation for anyone else. Using these techniques to lose weight may not be appropriate for you and your circumstances.

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