Stephaney Allinson BHMA, MNIMH, MCPP,
Medical Herbalist

There are different types of diabetes, the type I will be talking about here is Diabetes Mellitus. Also known as insulin dependent diabetes, most commonly known as either Type 1 or Type 2. This page is going to be discussing diet.
Different people get different levels of dietary advice with regards to diabetes from the NHS. I think it depends on where you are in the country and the individual practitioner involved as to how much information is given out about diet.
I have had conversations with people who have diabetes and they have had no conversation about diet at all, and some where they get able to get comprehensive info and a referral to a nutritionist. One thing that isn't necessarily directly related to diabetes is if you have poor blood sugar control, and that is not specific only to diabetics, it is very, very difficult to loose weight.

The most important thing you need to know about insulin dependent diabetes (both type 1 and 2) is that diet is incredibly important, it can, in certain cases, completely reverse type 2 and severely reduce the requirements for insulin in type 1. 
Which makes sense if you think about it, if you eat processed foods and sugar, you will need to increase your insulin intake and if you completely overhaul your diet and take all that out then you will need to use less. All changes in insulin should be closely monitored with the help of your healthcare provider. I have also had conversations with people who are doing everything right according to the information they have been given and their blood sugars are not going down. This is going to be because of their diet, the body turns carbohydrates almost directly into sugar, which is then dumped into the blood stream.

Once you have been diagnosed with diabetes, you need to change your lifestyle. This is a permanent change that will take time consuming planning. But make no mistake, it is a permanent change you need to make otherwise you are risking very severe, permanent, consequences to your health such as blindness, kidney problems and limb amputation. 

Avoid carbohydrates as much as possible, especially from processed and wheat sources. It is better to get carbohydrates from a potato rather than a slice of brown bread. This isn't a diet, it's a lifestyle change which is a big thing, you are doing this for the rest of your natural life. Below is a list of things that should be avoided entirely: 
White rice -  And anything that has white rice in it
Processed foods - including condiments, (Make your own instead) packet sauces, meats, ready meals, coated chicken etc
All sugar
Pop and energy drinks
Most cereal bars – check the sugar levels on some of the ‘healthy’ ones, you’ll be surprised at how healthy they actually aren’t.

Most breakfast cereals
Golden syrup
Maple syrup
Coffee - It really messes with your blood sugar levels.

Healthy fats such as coconut oil, nuts, avocados etc should to be a big part of your diet. You need to get out of the popular 'all fat is bad' thought process. This is complete rubbish and quite harmful. Cooking with coconut oil instead of olive oil for frying or roasting is much better for you and you should avoid margarine entirely.

Below is the list of foods you should pick from

Bitter salad vegetables such as rocket

Fresh fruit and vegetables - Organic or home grown as far as is practicable
Frozen fruit and vegetables - with the exception of something picked yourself, frozen fruit and veg are the freshest because they have to be frozen within 2 hours of being picked.
Nuts and seeds
Beans and pulses - All lentils, chick, garden and black eyed peas, baked, runner, fava, kidney, butter, haricot, cannellini, flageolet, pinto and borlotti beans and any others I have forgotten.
Fermented foods including traditionally produced tofu
Seed and nut butters
Brown rice
Lean meat - red and white
Probiotic yogurts – but do check the sugar in these
Herbs and spices

1 teaspoon of lemon juice in some water (generally hot is better but cold is ok) about a shot glass worth of water, drunk first thing in a morning as soon as you get up will work wonders to kick start your metabolism for the day.
Green veggies are a really, really good thing, spinach, kale, bok choy, broccoli, green peppers etc. They are also a very good source of calcium which your body processes far better than dairy sources. Hummus is a lovely thing to eat with veggies and very good for you. You can even use the juice from the chick peas as an egg substitute. It is also very quick to make your own (avoiding the processed again) and you can flavour it how you want with herbs and spices. One of the best choices  you can make is to eat seasonally, fresh strawberries do not grow in January for example and apples are not ripe in May.

Smoothies should be made up of 2/3 veg and 1/3 fruit. (And they should be smoothies, not juices because the vegetable and fruit fibres are important too.) Things such as spinach, bok choy, kale, rocket, avocado, carrots, peppers, broccoli etc should be in there along with fruit but avoid bananas if you can, they increase your histamine levels greatly so if you have any kind of allergy bananas make your body more reactive to that allergen.
Coconut water and coconut milk are good drinks the fat is very healthy and the milk and water are very hydrating and can be used to cook with.

When you do have a piece of fruit as a snack, have a few nuts or seeds with it (refer to healthy fats above) because the protein balances the blood sugar that is going to wobble with the fruit. Herbs and spices are a really good addition and very good for you generally, they help to digest food and calm inflammation as well as provide many other benefits. Add them at the end of cooking in small amounts so you don't lose the helpful constituents in the herbs.