I have a friend, very fit individual who changed diet only and now gets lightheaded when standing
what nutritional deficiency can cause this? He's low carb lacto paleo
When you eat low carb, especially at the beginning, it tends to have a diuretic effect. This, in effect, lowers the blood volume, which then lowers the blood pressure. When the blood pressure is low, it takes a few minutes for your body to "catch up" when rising from a sitting or lying position. Note to original poster: this is not a "nutritional deficiency" :-)
Have your friend add a little salt to his foods, and have him rise a little slower. His body will soon grow accustomed to the reduced blood pressure and it will learn to compensate for the lowered blood volume. This is not a dangerous condition.
NOTE: I am not a doctor. It's entirely possible he's dying of some strange malady of which I know nothing, but the people I know who have gone low carb (including myself) have this exact situation occur almost without exception.
I have had this problem too. It started after I lost a bunch of weight in the beginning of the year, and I naturally have very low blood pressure. I started fainting and getting seriously lightheaded every time I stood up. My cardiologist suggested staying hydrated, which made a big difference.
Then, after I went Paleo, it started happening again. I consulted with a nutritionist, who checked out my food logs. He suggested a fat imbalance is often a cause of postural hypotension. I have upped my fat intake with the "healthy" stuff - olive oil, almonds, etc, - and it has also made a difference.
Hope that helps!
I've been having a similar problem. I am always on the low blood pressure side, but recently it got worse... I am drinking a lot (could it be too much?), not counting calories, eating meat with fat and adding fat whenever I can.
I think I will use the suggestion of using more salt... I am eating carbs (even if pretty low, mostly from cream/cheese and veggies) so I am pretty sure it can't be too low carbs.
Have your friend had a chance to check his blood pressure at the moment? Could the weather be an issue? I know I feel much worse when there is a serious heat wave. Could it be over-training on cardio-like exercising? That's what hits me sometimes.
I would advise more observation - checking daily blood pressure at set times plus at moments of particular light-headedness and look for patterns.
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