Last year I took part in a unique television experiment. Doctor In Your House, on Channel 4 in the UK, involved me consulting patients in their own home rather than a surgery. It was an eye-opener, proving what I have known for a long time: patients don't always tell the full story to their GP.
Some things - how much we drink, or whether or not we have only "a couple of cigarettes a week" - can often deliberately be covered up.
Other things, such as diet, involve a healthy dose of self-deception. If you're honest with yourself, do you really "eat like a bird" yet still find you can't lose weight?
I have to say that I'm not here to judge. That's not a doctor's job. But the more truthful you are with us, the more we are able to help you.
Frank, candid discussions lead to better consultations, easier rapport with your doctor and better medical care in the long term.
With this in mind, here are the top five lies I'm told with alarming regularity by patients... and the reasons why it would be better all round if you just 'fessed up!
1. "I'm happy at work/in my relationship."
Bullying bosses, huge workloads and poor work-life balances have a lot to answer for in terms of ill-health. But people seem to vastly underestimate the effect this kind of stress can have. So when asked about work, don't brush it off as being "fine" if it's not.
Work is not fine if you have no time to relax or you dread going in. Likewise, a great deal of stress can be caused by an unhappy marriage or personal life.
It is not a sign of weakness or failure to acknowledge that your job or partner is making you miserable.
I regularly see patients who are starting to have physical symptoms during the week - or, paradoxically, only at the weekend when they finally relax and stop running on adrenaline - such as headaches or digestive problems.
We order rafts of blood tests and investigations, to no avail, only to later find out that in fact they work a 60-hour week and their relationship is collapsing.
If you tell us the truth, we can offer various kinds of help from stress management and psychotherapy, couples counselling, or even medication.
There is no blood test I can order for happiness so we need to know from you.
2. "I'm just loving parenthood."
This is a passion of mine. Parenthood is given such a rose-tinted write-up these days, especially on social media where people only ever boast about the good stuff, that it can be hard to admit things haven't gone to plan, that you hate breastfeeding, that your sex life is in tatters, that you feel like the only one whose baby never, ever sleeps.
The reality is that feeling utterly miserable after the birth - in both men and women incidentally, and not just for baby number one - is common, and certainly not something to be ashamed of.
I understand of course why people feel they have to lie about this to their doctor. There is a stigma as well as the guilt, and sadly a misconception that these feelings make you a bad parent or - even further from the truth - warrant social services involvement.
The earlier you ask for help with symptoms of low mood in any situation the better: it can take time to access the right help and we know early treatment for depression leads to better outcomes.
Being honest with a GP allows us to help you properly with medication, health visitor and family- centre support as well as sign-posting to the right therapy and support groups. It does not lead to social services or shame.
3. "Overweight? But I eat like a bird!"
My colleagues and I do actually hear this very phrase quite regularly. But I don't think patients always intentionally lie.
We all kid ourselves about the actual number of calories we consume. I know I do. Likewise having a gym membership is not the same as going to the gym.
The harsh truth is that, in most cases, being overweight is down to too many calories going in and not enough being used up.
Lying can also lead to inappropriate medical treatment.
As an example, if you have high blood pressure the current guidelines recommended lifestyle changes first - including exercise and dietary advice. If you claim to be doing this already, your doctor will bypass this stage and consider medication at an earlier stage.
This is medication that you may not need if your diet and exercise improved.
Poor diet and a lack of exercise in themselves are risk factors for cardiovascular disease and diabetes, and honesty means we can help you address that.
4. "I only drink/smoke at the weekends."
It seems to be written in law that you have to lie to your doctor about smoking and alcohol habits.
Clearly, this stems from the notion that as doctors we judge our patients' lifestyle, which is genuinely not the case.
So many patients say they drink at weekends when they really mean they get drunk at the weekends, and drink moderately all week.
The NHS quit smoking services have been hugely successful, and offer a low-cost way of giving up with good support.
Likewise many practices offer help with alcohol and sensible drinking advice.
But we need to know because smoking and alcohol are risk factors for disease - and not just the obvious ones such as lung cancer, but less well-known associations such as cervical cancer.
Knowing you have these risks helps us to make the best clinical judgment if you present with a potentially worrying symptom.
A persistent cough in someone we know is a smoker would warrant more thorough investigation than in a non-smoker.
5. "Yes doctor, I'm taking the pills."
I am not sure I understand why people lie to their doctor about the medicines they take.
Half of medicines returned to the pharmacy are actually unopened, which means there was no intention ever to take them.
If you are not taking your medicine, please be honest.
We understand people have a range of health beliefs and may not want a prescription of drugs at all - we would rather work with you to find an alternative solution than prescribe something you will throw away.
We can talk to you about other options rather than prescribing more and more, thinking our prescriptions are not taking effect.
I understand people may not want to even pick up a prescription because of the cost so please let us know as there can be ways of making it cheaper.
We also need to know if you are taking other medications we haven't prescribed - for example supplements bought on the internet or over-the-counter painkillers.
All of these can cause symptoms and interactions with other medications. It could be dangerous if you keep this information from your doctor.
So remember: we can only offer optimal care if we know the truth.