The FastDay Forum

Hi,

I've been on the fast diet for about a month. I'm 27, male, 169 cm and weigh around 83 kilos. I'm in my 5th week of the C25k running program so am jogging/walking 3 days a week and generally walk for 30 mins plus on the days I'm not jogging.

I should experiment a bit more before asking this question, but I guess I can update tomorrow when I'm eating more. Anyway it's my fast day today and I've been feeling a little dizzy, I've been checking my heart rate throughout the day and it's sticking around 38 bpm (just check it again, 41 now). I have been inactive each time I've checked though. Should I be worried about this? Should I not be fasting? Has anyone else had similar experiences?

[carorees]

Hi there and welcome to the forums!

For an athlete a low resting heart rate is good, as I'm sure you know. A low heart rate is less good if you have high blood pressure...do you know what yours is? I expect it is fine.

A low heart rate can cause dizzy spells as can low blood pressure and low blood sugar.

Are you eating up to TDEE on your feed days? With the exercise you are doing you should be eating plenty on feed days. I estimate around 2800 cals and 700 on fast days.

As you have experienced dizzy spells today I would break the fast now and have some carbs. Eat a healthy dinner tonight. Monitor your heart rate today and during tomorrow's feed day. Let is know what you find.

If your resting heart rate is low on feed days and you have no symptoms I shouldn't worry. If you continue to have symptoms on fast days I would consider increasing your fast day allowance a bit.

If you have symptoms on feed days too and/or an abnormal blood pressure I think you should get it checked out by the doc.

Thanks for the comments carorees.

I didn't end up eating for the rest of that day. I'm in Australia so it was close to bed time when I wrote it, didn't really want to eat another meal. The dizziness had gone away too. No idea what my blood pressure is like though, next time I go to the doc I'll get it checked. Heart rate stayed the same though., was 35bpm when I woke up.

Feed day today, haven't been dizzy and it's sticking between 60-70 bpms.

I might be eating too little, need to put a bit more effort into figuring out a diet plan. I'll see what it's like tomorrow though, got another fast day.

[carorees]

I think that if your normal heart rate is 60+ then 35 on a fast day is too low. How much did you eat? Next time make sure you have the full 700 allowed and that you are properly hydrated. Hopefully it was a one-off.

I ate around 600 calories. Didn't know I could have 700 on a fast day, but with these symptoms I guess I need to eat a bit more. Will have a bigger breakfast next time I fast. This is the first time this kind of thing has happened though.

[carorees]

You should work out your TDEE. With all the exercise you're doing it should be near 3000 I reckon & you can have 1/4 of that on fast days. Links to TDEE calculators in the FAQ (see my signature for FAQ link).

I have noticed that my resting heart rate drops quite a bit on fast days, but not to that extent! It tends to drop about 10-15bpm, from mid to high sixties to mid fifties. In my case I put it down to the digestive system not having as much to do as normal, and hence the heart not having to pump as much blood to the gut, but this seems quite extreme. I hope Caroline's advice helps!

http://www.ncbi.nlm.nih.gov/pubmed/17201801 reported an increased heart rate during 72h fasting of normal weight subjects.

An ADF trialhttp://jap.physiology.org/content/99/6/2128.long found that "The level of habitual daily physical activity did not decrease during fasting days. Thus the average heart rate during daytime was not different during fasting (79 ± 3 min−1) compared with nonfasting days (80 ± 3 min−1)."

In general there is little mention of heart rate in the clinical studies of fasting and intermittent calorie reduction. If reduced heart rate is not generally associated with fasting perhaps the OP has an underlying issue.