Regular exercise and good nutrition go hand in hand, and you might often see Personal Trainer's offering discount packages for exercise plans and nutrition plans together. Despite this, I'm here to explain why you should do your research before choosing a personal trainer (PT) to start training with, and why perhaps you should consider working with a dietician too for certain aspects of your health, and to notice the best results.
To put it simply, a PT ISN'T qualified to write specific meals plans for clients - in the same way a dietician/nutritionist isn't qualified to provide exercise plans. It's actually out of the scope of practice for a PT to do so; we can only offer nutritional advice, and any PT worth working with won't mind you asking. Saying this, we have a good understanding of nutrition and the benefits of a well-balanced diet with regards to improving training, or helping with weight loss for example. Nutrition is a huge section of what we study on our courses, but still not as in-depth as that of a qualified and recognised dietician.
A personal trainer shouldn't say to you "eat 20 grams of oats, topped with 1 whole medium banana and 2 tbsp of honey", but instead something along the lines of "a good breakfast to provide you with energy before a workout would be a small bowl porridge oats, a banana and a drizzle of honey.". The reason being is that everyone's diet and metabolism is different; what may be too much for one person may be too little for another. It sometimes even comes down to how different everyone's lifestyles can be - some jobs are desk based, so that person may need a different food intake to someone who is walking about on their feet all day, since they will have different goals and therefore need to eat different amount of calories in order to achieve their goal.
Use the government guidelines to look at portion size suggestions, or an app to help track your food. This way your personal trainer can make suggestions on how to improve your diet in relation to the type of goal you're trying to achieve. It's important to ensure that you diet is varied - a variety of carbohydrates, fats and proteins, as well as a variety of colours, minimum amounts of takeaway and alcohol, and shoud be matched with a decent exercise regime and good quality sleep.
PT's can help with nutrition towards weight management, and will be able to evaluate whether or not your diet is well-balanced to help towards your goal. In short, weight loss is achieved by a calorie deficit (burning more calories than are consumed), whilst weight gain - fairly obviously - is gained by calorie surplus (consume more calories than you burn). Muscle gain can be achieved by altering your levels of carbs, proteins and fats slightly, and it is best achieved from good quality proteins as opposed to shop bought shakes/bars that are consumed regularly.
Still, a PT may suggest alternative foods to try in order to eat a diet that is as varied as possible, but just take care when they start telling exactly how much of what to eat and when. When talking about nutrition and the advice that personal trainers can offer, the following quote comes to mind... "Give a man a fish and you'll feed him for a day. Teach a man to fish and you'll feed him for a lifetime." I believe that we, as PT's, should help our clients to create healthy habits that are personal to them in order for them to maintain a suitably healthy lifestyle - not use a "one diet fits all" method with suggestions that are just too specific, and that are not able to be maintained.
Ask your PT questions, and get their advice and knowledge, but make sure that you understand for yourself what it is you're doing with regards to nutrition. If you should decide that you want specific meal plans, or perhaps have a dietary requirement that involves a deeper understanding of nutrition, then consider asking a qualified dietician. There's nothing wrong with having help from both a personal trainer and dietician - as I said at the beginning of this post, regular exercise and good nutrition go hand in hand - it could be just what you need for a healthier (but still maintainable) lifestyle!