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The proverbial “sugar rush” that follows the consumption of a sweet treat is a well-known example of the potentially positive effects of food on mood.

On the other hand, the feeling of “hangry” – the phenomenon in which hunger manifests itself in the form of anger or irritability – illustrates that what we eat or don’t eat can also cause negative emotions.

Recent research suggests that fluctuations in blood sugar levels are partly responsible for the link between what we eat and how we feel. Through its effects on our hormones and nervous system, blood sugar levels can contribute to anxiety and depression.

Mental health is complex. There are countless social, psychological and biological factors that ultimately determine a person’s life. However, numerous randomized controlled trials have shown that diet is a biological factor that can significantly influence the risk of symptoms of depression and anxiety, especially in women.

As a family medicine resident with a PhD in nutritional science, I have seen that antidepressants work for some patients but not for others, so I believe treatment strategies for mental illness should target all risk factors, including diet.

The role of the glycemic index

Many of the randomized controlled trials that have demonstrated the link between diet and mental health have tested the Mediterranean diet, or a slightly modified version of it. The Mediterranean diet is typically characterized by plenty of vegetables—particularly dark green leafy vegetables—fruit, olive oil, whole grains, legumes, and nuts, as well as small amounts of fish, meat, and dairy. One of the many features of the Mediterranean diet that may account for its effect on mood is its low glycemic index.

The glycemic index is a system that ranks foods and diets according to their potential to raise blood sugar levels. Consistent with the observation that blood sugar fluctuations affect mood, high-glycemic index diets that cause drastic spikes in blood sugar have been linked to an increased risk of depression and, to some extent, anxiety.

High glycemic index carbohydrates include white rice, white bread, crackers and baked goods, so a diet high in these foods may increase the risk of depression and anxiety. Low glycemic index carbohydrates, such as parboiled rice and al dente pasta, are absorbed more slowly and cause a smaller rise in blood sugar, which is associated with a lower risk.

How nutrition affects mood

Many scientific mechanisms have been proposed to explain the link between diet and mental health. One plausible explanation that links blood sugar fluctuations to mood is their effect on our hormones.

Every time we eat sugar or carbohydrates like bread, rice, pasta, potatoes and crackers, the resulting rise in blood sugar levels triggers a cascade of hormones and signaling molecules. For example, dopamine – our brain’s happiness signal – is the reason we may experience a “sugar rush” after eating desserts or baked goods. Dopamine is the body’s way of rewarding us for consuming the calories or energy necessary to survive.

Insulin is another hormone triggered by carbohydrates and sugar. Insulin’s job is to lower blood sugar levels by moving the sugar we eat into our cells and tissues so that it can be used for energy. However, when we eat too much sugar, too many carbohydrates, or carbohydrates with a high glycemic index, the rapid rise in blood sugar causes insulin to rise drastically. This can cause blood sugar levels to drop below baseline.

This drop in blood sugar levels triggers the release of adrenaline and its cousin noradrenaline. Both hormones send glucose into the bloodstream to bring blood sugar levels back to the right level.

But adrenaline doesn’t just affect blood sugar levels. It also affects how we feel, and its release can manifest itself in anxiety, fear, or aggression. So diet affects mood through its effect on blood sugar levels, which in turn triggers the hormones that determine how we feel.

Interestingly, the adrenaline surge that occurs after eating sugar and carbohydrates doesn’t occur until four to five hours after eating. So when we eat sugar and carbohydrates, dopamine makes us feel good in the short term; but in the long term, adrenaline can make us feel bad.

However, not everyone is affected equally. The same meals can cause very different blood sugar responses in different people, depending on gender, genetics, lack of exercise and gut microbiome.

And it’s important to remember that, as mentioned earlier, mental health is complicated, so in certain circumstances no amount of nutritional optimization can overcome the social and psychological factors that may underlie the experience.

However, poor nutrition can certainly lead to a deterioration in a person’s wellbeing and is therefore relevant to everyone, especially women who want to optimise their mental health. Research has shown that women in particular are more sensitive to the effects of the glycemic index and diet overall.

Unfortunately, simple solutions like replacing sugar with artificial sweeteners are not an option. Research has shown that of all processed foods, artificial sweeteners and artificially sweetened beverages are most strongly linked to depression.

Mood optimization through food

The most obvious way to stabilize blood sugar levels is to reduce sugar and carbohydrate intake. However, this is not the only way. Research has shown that simple changes can dramatically mitigate the wild swings in blood sugar levels. Some strategies to stabilize blood sugar levels and optimize mood include:

• Make low-glycemic index carbohydrates like parboiled rice, whole wheat bread, and al dente cooked pasta your staples, and be mindful of how many high-glycemic index carbohydrates you eat. I give my patients this guide to make them aware of the glycemic index of different carbohydrates.
• Eat carbohydrates earlier in the day, such as at breakfast or lunch, rather than later in the day, such as at dinner or, even worse, as an evening snack. Our hormones follow a circadian rhythm and carbohydrates eaten earlier in the day will cause a smaller rise in blood sugar than carbohydrates eaten later in the day.
• Avoid eating carbohydrates alone, such as snacking on a packet of crackers or wolfing down a bowl of rice. Always try to combine carbohydrates with proteins such as beans, nuts, meat and fish, or with healthy fats such as olive oil and avocado. The combination of nutrients slows down the digestion of the carbohydrates, thereby leading to a smaller rise in blood sugar.
• Eat carbohydrates at the end of the meal, after eating vegetables and proteins first. Simply changing the order in which foods are eaten can dramatically reduce the subsequent rise in blood sugar.
• Before eating carbohydrates, eat a salad dressed with olive oil and vinegar. The combination of vegetables, acid from the vinegar and fat from the olive oil work together to slow down the absorption of carbohydrates and minimize the resulting rise in blood sugar.