I was talking to a son of a friend of mine over the weekend. Mark (not his real name) is 18 and has been finding his energy and motivation can flag at times. Some of the time he can be energised and motivated. Other times he feels lethargic and “can’t be bothered with life”. Naturally, the focus on this issue has been on his life circumstances, but I was also interested to explore if physiological or biochemical factors may be playing some part in his symptoms.

I asked Mark if his symptoms appeared to have any relationship to food. He said others had noticed that his mood improves, at least momentarily on eating. There are many reasons why someone may feel cheerier for eating including, of course, the deriving of pleasure from food. One other important reason individuals may feel better for eating is that they have come into that meal with low levels of blood sugar (hypoglycaemia).

Because the brain generally uses a lot of sugar, under-fuelling of the brain through hypoglycaemia can cause it to malfunction. Low mental energy and low mood are potential symptoms of hypoglycaemia. When blood sugar levels are improved by eating, it can lead to an improvement in energy and outlook too.

I have found over the years that blood sugar instability is a major cause of fluctuation in mood and energy. This has not just been my professional experience, but my personal experience too. Many years ago (when my diet was much richer in carbohydrate) I was quite prone to what I take to be spells of hypoglycaemia myself.

While I talking to Mark I remembered how I would sit as medical student in teaching hospital clinics or lectures in the afternoon (a danger time for hypoglycaemia) feeling tired, unable to concentrate and often utterly demotivated. Later on I began to realise that at least a large part of these issues were down to my awry blood sugar control. This was picked up on by others too. For example, if I was grumpy those who knew me well (a girlfriend, say) would urge me to ‘eat something’. One of my friends, a doctor, suggested that I was Snow White’s eighth dwarf – going under the name of ‘hypo’.

I have learned, likes many others, that getting the diet right is key to stabilising blood sugar levels. There are two fundamental here: eating foods that release sugar relatively slowly into the bloodstream, and eating those foods regularly enough.

I asked Mark about his diet. A lot of his diet turned out to be generally disruptive for blood sugar (Subway sandwiches, burgers and fries, mounds of pasta). His eating was also quite irregular. I asked about breakfast. His reply was “I don’t see the point of breakfast”. I asked him what he meant by this and he replied “When I eat breakfast I’m starving an hour later.” When I asked him what he might have for breakfast it turned out to be cereal.

His experience here is relatively common. I quite often hear individuals tell me they are hungrier in the morning after the eat breakfast than if they don’t. This, I think, is another symptom of impaired blood sugar regulation. Typical breakfast fare such as toast and cereal tend to induce surges of blood sugar which, in turn, can cause large quantities of insulin to be secreted by the pancreas. One of the chief functions of insulin is to reduce blood sugar levels, but a glut of insulin can cause hypoglycaemia, which can cause individuals to be hungry (typically for carbohydrate-rich foods).

My advice was to scale back the carbs a bit, up the protein, and to eat more regularly (including healthy snacks if he gets peckish between meals). Cutting back on carbs and eating more regularly should help to ensure a steadier supply of fuel into the brain. More protein should help here too. But another trick that protein has up its sleeve is the fact that it is made of amino acids, and these supply the building blocks of brain chemicals (neurotransmitters) that can have a profound effect on mood and brain energy (including dopamine, noradrenaline and serotonin).

Giving advice is no guarantee that someone will act on it. However, my experience tells me that if Mark adjusts his diet in the way I outline here he will see quite immediate benefit in terms of his energy and mood. I know it did with me, and I’ve seen it work for countless others too.