I have purposefully refrained from entitling this section ‘Diet’; hopefully by the time you have reached the end you will understand why. There is no prescription food list for people with diabetes!
Current recommendations for people with diabetes are in line with those for the general population i.e. ‘eat a healthy and well balanced diet’. You will no doubt have read elsewhere that healthy eating for people with diabetes is no different from healthy eating for a person without diabetes. However, in my opinion the current ‘recommendations’ are misleading for they do fail to emphasise the central issue – that of blood glucose control.
The ultimate goals are, of course, to attain good blood glucose levels, blood lipid levels and blood pressure levels and to reach and maintain a reasonable body weight – all of which will minimise the development of further health problems (see the section on ‘Control‘). In addition, optimal nutrition will improve general health and well being.
Diabetes presents as a higher than normal blood glucose level. The reasons behind this differ between people with Type 1 and the broad spectrum of diseases classed as Type 2 diabetes. Firstly, you need to be clear in your own mind as to the type of diabetes that you have, and therefore what might be contributing to your high blood glucose level. Then you should become more clear about what your dietary objectives are, and how to achieve them.
If you have Type 1 diabetes you are not likely to be producing any insulin yourself and you will be taking insulin injections. Your insulin does two important jobs – it allows your body’s cells to take glucose from the bloodstream and burn it for energy. It also allows your body’s cells to take up and store glucose after a meal. Normally the body would fine tune its insulin secretion to your activities. Now YOU have to take over and be your beta cells to the best of your ability.
Let’s take a quick look at what we’re dealing with. In simple terms, on the one side we have insulin injections and physical activity lowering blood glucose and on the other side we have dietary consumption raising blood glucose. The long and the short of it is that you have to balance these, both in terms of quantity and timing, to keep your blood glucose levels as near normal as possible. To achieve this, you will need to learn about self monitoring of blood glucose.
Your primary objective then, is to equate the digestion of the food you eat to the absorption of the insulin you inject. You need to know which components of your diet contribute to blood glucose level, to what extent, and when.
If you have been diagnosed with Type 2 diabetes the situation is less clear cut. Your blood glucose levels are high and you have been diagnosed with diabetes. You are likely to be producing some insulin but how much and under what circumstances? Further complicating matters is the issue of insulin resistance. Are your blood glucose levels high because your beta cells are just not producing enough insulin, or because your body is not responding to your insulin? Perhaps both of these factors are true.
Normally insulin is secreted throughout the day at a ‘basal’ or ‘background’ level. This allows the body’s cells to use glucose from the blood. When the blood glucose level starts to rise, for example, after a meal, more insulin is produced which enables the body’s cells to take up and store the glucose from the meal. The insulin response to a meal consists of an initial burst of insulin, followed by a prolonged raised level of secretion which persists whilst the meal is being digested. These two components are often referred to as phase 1 and phase 2 insulin responses. In many people with Type 2 diabetes, the phase 1 insulin response is often markedly reduced or absent altogether. If this is so in your case, then this may affect the type of foods you choose.
One of your first considerations should probably be whether or not you are overweight. The body mass index (BMI) is a commonly used measurement of obesity that takes height into account. It does not, however, take muscle mass into account. A BMI of 30 kg/m2 defines clinical obesity. An ideal BMI would be in the region of 25 kg/m2 for men, 24 kg/m2 for women. If you are significantly overweight then this will probably be contributing to insulin resistance; if you can manage to lose weight and increase your muscle:fat ratio then you’re off to a fine start. Your own insulin production may then be able to keep your blood glucose levels in check.
So, if you are overweight, one of your main dietary objectives may be to restrict calorie intake with the aim of shedding a few kilos.
Another important consideration is that of medication. If you are taking tablets for your diabetes, then you may need to take these into account when considering your diet. If you are taking medication that encourages the beta cells to produce insulin (e.g. a sulphonylurea), then you may be at risk of hypoglycaemia (low blood glucose) if you do not eat sufficient at the appropriate time. And if you are taking insulin then you most certainly will have to take this into account.
So, if you are taking medication that lowers the blood glucose of its own accord, then your dietary objectives should include consideration of timing and quantity of food.
You should also strive to learn which components of your diet raise your blood glucose level, and when. For this you will need to learn about self monitoring of blood glucose.
What constitutes a ‘healthy diet’ then? Firstly, we need to take a look at the basic components of food – carbohydrates, fats, protein and ‘micronutrients’ (i.e. vitamins and minerals). All of these are essential for a healthy, balanced diet. Most foods contain mixtures of two or more of these nutrients; you may need to start consulting food labels and perhaps invest in a ‘calorie counter’, or similar book.
Dietary carbohydrates come in the form of sugars, starchy foods and fibre. Carbohydrates provide the body with its main source of energy – glucose. Sugars and starches are the main contributors to blood glucose.
Sugars are often referred to as ‘simple carbohydrates‘. There are a number of different types of sugars:
|Single sugars (monosaccharides)|
|Glucose||Also called ‘dextrose’.|
|Fructose||Also called ‘fruit sugar’|
|Galactose||Mainly from milk, but also a component of pectins and gums.|
|Glucose, fructose and galactose are absorbed directly. Fructose and surplus to the body’s requirements may then be converted to glucose in the liver.|
|Double sugars (disaccharides)|
|Sucrose||‘table sugar’. A sucrose molecule consists of a glucose and a fructose joined together.|
|Lactose||‘milk sugar’. A lactose molecule consists of a glucose and a galactose joined together.|
|Maltose||A maltose molecule consists of two glucose molecules joined together.|
|Sucrose, lactose and maltose need to be broken down by digestive enzymes before their component sugars can be absorbed.|
Sugar is frequently referred to as a source of ’empty calories’. Large amounts of sugar – and therefore calories – can easily be consumed with minimal effect in terms of suppressing appetite. Additionally, foods such as sweets and sugary soft drinks have little nutritional value; in other words they contain few vitamins and minerals.
Starches are the plants way of storing the glucose they make (from carbon dioxide and water in the atmosphere, using sunlight as energy for the chemical reaction). Starch is the equivalent of glycogen, which is our storage form of glucose. Starches are basically comprised of a mixture of long straight chains of glucose units (amylose) and branched chains of glucose units (amylopectin).
Starches or ‘complex carbohydrates‘ can be found in grains and foods derived from grains – bread, cereals, pasta. Root vegetables, such as potatoes and parsnips are also a source of starch.
Dietary fibre is often classified according to its solubility in water. Soluble fibre is founds in oats, pulses, and citrus fruits and includes pectins and gums. Insoluble fibre is mainly cellulose (a major component of plant cell walls); this type of fibre can be found in wheat bran, nuts, grains and vegetables.
Soluble fibre is fermented in the gut, producing gases. Insoluble fibre remains largely intact as it passes through the digestive system and adds to the volume of stools.
Increased consumption of soluble fibre has been reported to decrease LDL cholesterol levels and may be useful in the prevention of heart disease. Insoluble fibre is thought to be beneficial in the prevention of constipation, haemorrhoids (piles) and colon cancer.
Fats are an important source of energy and provide essential components for cell membranes and for hormones and other signalling molecules. Dietary fat is also necessary for the absorption of some fat soluble vitamins.
A high intake of fats may contribute to elevated blood lipid levels and an increased risk of atherosclerosis (hardening of the arteries) and heart disease. Fats contain more calories, weight for weight, than carbohydrates or protein – a diet high in fat may therefore encourage weight gain and lead to obesity. For these reasons, classical nutrition guidelines recommend that we eat less fat.
Fats are composed of fatty acids and glycerol. Three fatty acids and one glycerol molecule together form a triglyceride. Fats are further classified according to the structure of the fatty acids.
|Saturated fats||Monounsaturated fats||Polyunsaturated fats|
A diet high in saturated fats can lead to increased cholesterol levels. The Framingham Study showed, without a doubt, that high blood cholesterol levels are linked to heart disease. The ratio of polyunsaturated to saturated fat in the diet is important in controlling the synthesis of cholesterol in the liver. It is therefore recommended that you reduce your intake of saturated fat and increase the amount of polyunsaturated and monounsaturated fat.
Many foods high in fat are also high in saturated fat – choosing the low fat option will therefore help to avoid, or at least reduce, saturated fat intake.
Protein is important for maintaining many structural elements in our bodies, including muscle and bone. The building blocks of protein molecules are called amino acids; there are twenty of these – some we can manufacture ourselves, others are essential to our diet.
Sources of animal protein include meat, fish, poultry, eggs and dairy products. Nuts and seeds are good sources of vegetable protein.
Micronutrients are otherwise known as vitamins and minerals. They are an essential part of a healthy diet, but usually required only in small amounts. Some vitamins are soluble in fats and can only absorbed from the gut when dissolved in lipids; others are water soluble:
|Fat-soluble vitamins||Water-soluble vitamins|
Trace elements are also important – these include cobalt, iodine, selenium, iron and zinc and are often referred to as ‘minerals’.
Other inorganic nutrients that we require include sodium, potassium and calcium. (Note that sodium intake may need to be reduced if blood pressure is high.)
Current recommendations suggest that our total calorie intake should be distributed approximately as follows:
- 55 % from carbohydrates
- 30 % from fat
- 15 % from protein
Calories (kcal) are a unit of energy. If we do not use the food we eat for energy then it will remain in storage in our bodies, for the long term as fat. So effectively, if we do not burn off about the same number of calories as we consume, then we either lose or gain weight. (Don’t panic, you don’t need to go for a five mile run to burn calories, our bodies use a great deal of energy just ticking over, even whilst we are asleep.)
Carbohydrates and protein provide approximately 4 calories per gram (kcal/g) whereas fat provides 9 kcal/g. This is why the ‘fat is fattening’ concept has arisen – because, weight for weight, fat provides almost twice as many calories as carbohydrate or protein.
So, by weight (… per 100g food), the current recommendations can be interpreted as:
In order to lose weight, it is recommended that total daily calorie intake is reduced by 50 – 500 calories.
How Foods Affect Blood Glucose Levels
It is imperative that you learn how different foods affect your blood glucose levels. Remember that we are all different; ultimately it is up to you to write your own rulebook.
The term ‘digestion’ simply refers to the breakdown of the food we eat into molecules which are small enough to be absorbed or transported through the lining of the gut. Digestion involves a large number of enzymes and actually starts in the mouth with saliva. Further digestion takes place in the stomach and the first part of the small intestine.
|Food component||Products of digestion|
|Starches and sugars||Glucose, fructose, galactose|
|Fats||Fatty acids, glycerol|
Factors affecting digestion
For the digestive enzymes to do their job, they need to be active and for this the environment needs to be just right – the stomach contents should be appropriately acidic, for example. Also remember that an enzyme molecule needs to come into contact with the food molecule before it can break it down; this is why increasing the amount of indigestible material you eat (i.e. fibre) will slow down the digestion of starches and therefore slow down the rate that glucose appears in the blood after a meal.
Some people with neuropathy (see section on Complications) may suffer from delayed emptying of the stomach which will affect the digestion and absorption of food.
Many people tend to associate diabetes with a sugar-free diet – this is something of a misconception. It used to be thought that, when eaten alone, simple sugars raised the blood glucose level rapidly because they require little digestion. We now know that this is not entirely true – there actually seems to be little difference in the rate of digestion of simple versus complex carbohydrates. A cautionary note though:
By ‘simple sugars’, I am really referring to sucrose. Glucose does not require digestion at all, and will usually be absorbed rapidly. It is therefore important that you learn to distinguish between the different types of carbohydrates and sugars (and read food labels).
Complex – as opposed to simple – carbohydrates remain the preferred source of carbohydrate because they are more likely to contain fibre and micronutrients.
Our digestive system houses a number of enzymes which break bonds between glucose molecules in starch. When free, single glucose units can then be taken up and into the bloodstream. The rate at which starch is broken down into glucose molecules will depend on its composition in terms of amylose (straight chain) and amylopectin (branched chain) units.
Different carbohydrate foods are known to affect blood glucose levels in different ways; in an attempt to quantify these differences the ‘glycaemic index’ (GI) has evolved. This, in theory, provides a measure of the magnitude of the increase in blood glucose level that a given amount of a given food will cause. Foods are ranked between 0 and 150, usually against white bread at 100. Foods with a low GI (e.g. pearl barley) cause less of an excursion in blood glucose compared to those with a high GI (e.g. glucose).
How is the GI factor derived?
The GI for a given food is usually obtained as follows: 50 g of carbohydrate of a given food (e.g. cornflakes) is eaten and the blood glucose level is monitored over the following two hours. A simple plot of blood glucose against time can be drawn; the area under the curve is then compared to that obtained from the ‘standard’ (usually white bread).
How do we make use of the GI?
The clinical utility of the GI is still debated. At the centre of the debate lies the issue of whether GI values hold true for mixed meals. Some people believe that ‘a carbohydrate is a carbohydrate…’ and that GI values have little practical significance for the diabetic. I beg to differ. The GI can be a very useful tool; the problem is in defining its role and fitting it into dietary practices such as carbohydrate counting.
High GI foods may cause post meal spikes in blood glucose in people with Type 2 diabetes who are lacking the phase 1 insulin response; such people may benefit from choosing low GI foods to base their meals on.
Some people, especially those using the new fast acting insulin analogues, such as Humalog, may find that substituting low GI foods for high GI foods actually result in post meal hypoglycaemia. These fast acting insulin analogues were developed in order to combat the post meal spikes in blood glucose arising from conventional carbohydrate intake at mealtimes.
There are, of course, some instances when ‘fast-acting carbohydrate’ is required and people with diabetes may actually need eat something that will rapidly raise their blood glucose level:
- to correct hypoglycaemia
- to prevent hypoglycaemia during periods of exercise
We have no storage depots of protein, so amino acids surplus to the body’s requirements are eventually converted to glycogen in the liver. Under some circumstances then, protein becomes a potential source of blood glucose.
Some sources quote that approximately 50% of dietary protein eventually appears as blood glucose. As a result it has been suggested that dietary protein should be calculated and ‘covered’ by insulin, in a similar manner to carbohydrate. In my opinion this is dangerous practice, especially if using short acting or, worse still, fast acting insulin. Any rise in blood glucose which is attributable to dietary protein will occur several hours after eating. If, I repeat IF, any alterations to insulin are made to accommodate large amounts of protein eaten, then it might be more appropriate to make a small change in the dose of long acting insulin.
The digestion of dietary triglycerides yields glycerol and fatty acids. Storage of fatty acids in adipose tissue re-incorporates one molecule of glycerol with three fatty acids. However, the fatty acids may be used by the body, in which case, surplus glycerol will then be converted to glycogen in the liver. Under such circumstances, a small fraction of dietary fat may, ultimately, contribute to blood glucose level. Usually, however, this will be negligible. Some sources quote as much as 10% of dietary fat contributing to blood glucose level; this assumes that all glycerol is converted to glucose, rather than the surplus.
Perhaps a more significant effect of fat on the blood glucose control is related to its physical presence in the gut. Carbohydrates and proteins are digested in the stomach and first part of the gut. Fats are digested and absorbed further down the line. Significant amounts of dietary fat can therefore slow down the digestion of carbohydrate and subsequent absorption of glucose into the bloodstream. Fatty foods may also delay the empting of the stomach, which in turn will delay digestion and absorption of food. The magnitude of these effects varies between individuals and also depends on the types of foods consumed.
Eat small amounts regularly throughout the day
Enjoy a wide variety of foods
Eat lots of fruit, vegetables, and wholegrain cereals
Choose low-fat or Lite options where possible, and restrict saturated fats
Avoid eating too many sugary foods on a regular basis – sweets, buscuits, cakes, chocolate and candies – but do enjoy the occasional treat
Choose low-salt foods, and use salt sparingly
Eat plenty of low-fat dairy foods containing calcium (especially women)
Look for iron-containing foods (especially girls, women, athletes, vegetarians)
Moderate your alcohol intake
Avoid rapid weight loss plans, and very restricted diets… Enjoy your life, and enjoy your food!
The successful approach to ‘food choices’ in diabetes will usually revolve around some kind of meal plan. The phrase ‘meal plan’ is enough to put anyone off – you might see it in a more positive light if you think of it as your action plan. This will necessarily incorporate your objectives.
In summary, here are some of the more important considerations:
- A well balanced and nutritious diet is a giant step in itself towards improved general health.
- Try to maintain day-to-day consistency with the timing, amount and types of food that you eat .
- Use snacks to prevent hypoglycaemia, during or after periods of increased activity.
- Consider your insulin type and action profile in relation to the timing of your meals and snacks (see section ‘Using Insulin’.
- Moderate – rather than severe – restriction of your food intake will improve the chances of success, especially with respect to permanent weight loss.
And finally, perhaps most importantly…
- Ascertain how and when different food types affect your blood glucose levels with frequent blood glucose testing.