Hydration is the key to beating feelings of dizziness and nausea while exercising.

Dear Dr. Benson,

I work out three to four times per 5 day week and keep fairly active on weekends. Of late, I’ve been experiencing some light-headedness while doing weights, and a few times following workouts have been experiencing nausea or vomiting.

A deciding factor in the nausea episodes seems to be where I work out, as the upstairs area of the gym has lots of air conditioners and the downstairs area has a low roof and feels quite hot, and although I do different exercises in both locations, there are some cross-overs during which I find I have less trouble in the better ventilated area. Dizziness has been experienced at both. There are occasionally times it has been experienced during the working day, although this normally follows periods of high stress or poor sleep, so I have not really been highly concerned with it. I’m also experiencing lethargy far earlier in my workouts that I was a few months ago.

I’m not sure if it’s a dietary thing or if it’s something I should see a GP about. It’s certainly the case that if my food consumption is slightly increased, I experience dizziness less frequently, although if I increase it significantly, then vomiting and nausea increases during workouts (this, I assume, is more related to undigested food in the stomach as blood is diverted to the muscles than to anything else).

I take protein supplements post-workout and occasionally pre-workout if I lack the time at work for a mid-morning snack. My first meal is usually around 8am and the post-workout consumption is about 1pm, sometimes 2pm. Consistency of mid-morning meals is erratic at best- maybe one day out of five, as usually I get swamped with work.

Is this likely to be a simple case of needing a greater energy intake? Could it be related to blood sugar? Or should I consider seeing a GP just in case?

Kind regards, 


Dear Reuben,

Obviously it would be important for you to see your GP for a basic check up and blood tests to rule out any significant problem.  If these episodes of dizziness, nausea and vomiting are also associated with headaches for example, your GP should do a thorough neurological examination to ensure that there is no intracranial pathology.

However it is possible that your symptoms are related to either the environment, as you have identified with it being more likely to happen in hotter, less ventilated areas; or occasionally these symptoms can be due to hyperventilation that occurs in some people when they work out and lift heavy weights, so ensure your breathing is slow and controlled.

More possible though I feel that it may actually be the result of low blood sugar and/ or some dehydration during your workouts, which leads us to a good discussion on exercise hydration and nutrition advice…

The fluid and energy you consume before, during, and after an exercise session are all equally important, not only to optimise your performance (and hence the effectiveness of your work-out), but also to maintain comfort and hence make the experience more enjoyable.


Before exercise it is important to drink at least 500mls of water in the 2 hrs leading up, including 200mls of water  in the 15 minutes before starting;

You also need to eat an easily digested carbohydrate 1-4 hours leading up e.g. fruit such as banana, pasta, potato, rice, breakfast cereal, etc.

Protein is too heavy pre-exercise, and won’t provide a source of quick acting energy.

During exercise you should aim to drink at least 200mls of water or sports drink every 20 minutes.

If you don’t use a sports drink, make sure you have some form of quickly digested carbohydrate at least once an hour e.g. fruit, sports bars etc.


After exercise you should drink at least 500-1000mls of water in the 2 hours following

(until your urine is clear!), and eat a source of carbohydrate and protein e.g. fruit smoothie, nutritional supplement drink, yoghurt, etc.

If you are trying to gain muscle, adding protein powders is useful here.


After studying medicine at the University of Sydney, Benson spent a number of years gaining significant critical care experience by working in hospital emergency departments, before undertaking general practice training. He has a broad experience in military medicine (civilian medical officer for the Royal Australian Navy), telehealth (senior doctor for the federal government’s after-hours GP helpline), women’s health, travel medicine and executive health (medical director of a national corporate health company). He's a strong advocate for science-based medicine, with a passion for preventive health.

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