I have regular blood tests because I have a rare immune condition and I know I'm lucky to get them, they are a useful guide. My experience of GPs is that it's usually very difficult to get blood tests done, a GP once said airily to me 'do another blood test next day and you'll get a different result'!
It's true that there is a lot of conflicting advice out there which is why I said that the best guide is whether or not a vitamin/multivitamin seems to go some way to sorting out the problem that you feel you have.
Similarly I have discovered that a low carb diet suits me, it stops my blood sugar levels swinging and keeps weight off my middle. Low carb, not extremely low, and avoiding dairy both obviously suit my constitution. It's not very difficult to adjust diet, I do think it's important to listen to your own body. Unfortunately, many medications cause long term side effects if you take them regularly. Someone mentioned ibuprofen, a GP told me long ago that they can seriously affect the kidneys.
I've never heard of Dr Ali but I just looked him up and his book sounds interesting: here's the description:
by Dr Mosaraf Ali (Author)
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Each one of us is unique, so it makes sense that no single diet will work for everyone. In Dr Ali's Nutrition Bible, physician to the stars and bestselling author Dr Ali offers a pioneering new approach to eating, based on working with the features that make you who you are. You can dramatically improve the way you feel by using the easy-to-follow programmes devised to let you choose the best foods for you. --Learn all of the nutritional basics such as creating a balanced diet and obtaining essential vitamins and minerals--Adjust your diet according to your age, gender, temperament, lifestyle and your state of health--Plan your meals around the seasons --Give your body a well deserved rest by detoxing--Discover dietary solutions to a range of health problems, including diabetes, colds and flu, irritable bowel syndrome, arthritis, osteoporosis, high blood pressure, anxiety and eczema