Eating for energy: food that boosts your productivity

Are you eating your way to a post lunch-slump?

Nutritionists say unwise food choices at lunch can shorten your attention span in the afternoon, so try keeping down the carbs and watch your energy level rise.

It’s the after-lunch session of the conference and, despite your best efforts to switch on, you feel a brain-fog descend and your eyelids droop as you realise you have no idea what the presenter has just said.

The post-lunch slump – we have all felt its sleep-inducing effects. In fact, we’ve been struggling with it for thousands of years. In 350BCE, the Greek philosopher Aristotle noted in his essay “On Sleep and Sleeplessness” that “fits of drowsiness are especially apt to come on after meals”.

Is food the cause of the post-lunch slump and, if so, could a better choice of food be part of the solution?

Lynell Peck, director of culinary services at Sydney’s new International Convention Centre (ICC Sydney), believes so. With the help of a nutritionist, she and her team have devised ICC Sydney’s Feeding Your Performance philosophy. It comes with a specially designed menu promising to keep conference delegates bright and alert well into the afternoon. 

“We aim to limit refined starchy foods such as bread and white sugar, and offer smaller portion sizes with plenty of local fresh vegetables, salads, herbs and plant sources of protein,” says Peck. “We also offer botanical and coconut waters to help keep people hydrated.”

“I would go into a carb coma and feel like a zombie.” Kane Munro CPA

Kane Munro CPA, director of cloud-based Accountancy Online in Melbourne, says ICC Sydney’s fresh and healthy menu “is a great idea”. He has first-hand experience of the productivity benefits of choosing different lunch foods. Before making the switch to lower-carbohydrate choices, Munro would have a roll from a Subway franchise, or a hamburger and chips, or toasted sandwiches for lunch. 

“About 90 minutes later I would go into a carb coma and feel like a zombie,” he says. “Then I’d reach for something sweet – an apple scroll was my favourite – which would give me a buzz for about half an hour, but afterwards I’d feel even worse.”

Munro started looking for something that would help keep his energy constant. “When you run your own business, every minute counts,” he points out.

Today it’s chicken breast and steamed vegetables for lunch. “It’s made a really big difference. I now work better for longer and don’t even notice the slump.”

Why energy clocks off

As for the causes of the post-lunch drop in energy, they are not all about food type. Due to our 24-hour circadian rhythms, we naturally experience a dip in alertness in the early afternoon, whether we eat lunch or not, and this complicates any interpretation of the impact of meals.

Then there’s the toll digestion itself can take on energy levels. When food enters the stomach, the body shunts blood away from our brain to the intestines to assist with digestion. With less blood going to central control, we can feel tired. The larger the meal, the bigger the energy drain.

The fact that the digestive load of lunch generally coincides with a circadian dip in energy is all the more reason to explore ways to reduce its effects.

Carbs curb your brainpower

How much difference does the nutrient content of lunch have on our subsequent energy? We know that over the long term, good nutrition offers immense benefits to the body and brain, including improved cognitive performance for those who eat lots of fruit and vegetables.

However, can food have an immediate effect on our alertness? Is there a scientific explanation for Munro’s “carb coma”?

In the 1970s, Dr Richard Wurtman of the Massachusetts Institute of Technology helped to explain carbohydrates’ soporific effect when he documented changes in the brain chemistry of rats fed high-carbohydrate diets. 

High-carbohydrate foods are broken down into glucose in the blood, which stimulates the release of insulin. This results in a relatively higher level of circulating tryptophan, which is taken up by the brain and converted to serotonin, a relaxing, feel-good hormone that can also induce drowsiness. Wurtman’s subsequent research found the same biochemical pathway in humans.

It’s the high glycaemic index (GI) carbohydrate foods, such as potatoes, short-grain rice and white bread, that cause the biggest rise in blood tryptophan (and presumably serotonin), according to a 2011 University of Sydney study by Christopher Herrera and others, published in the British Journal of Nutrition

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It followed a 2007 study by the university’s Chin Moi Chow and her colleagues, published in the American Journal of Clinical Nutrition, which showed the sleep-inducing effect of a high-GI meal was so great that if consumed for dinner, it nearly halved the amount of time it took subjects to fall asleep at night.

Low-GI foods, such as legumes and some grainy breads, release glucose into the blood stream much more slowly. They will still affect serotonin levels, but to a lesser extent and over a longer period of time, according to Robbie Clark, sports dietitian at the online clinic The Health Clinic.

On the ICC Sydney menu you’ll find low-GI carbohydrate choices such as spiced oats, pearl barley, curried lentils and freekeh, a form of green wheat that is high in protein and fibre.

High-protein foods can offset the effect of carbohydrates and help keep us alert by contributing less tryptophan to our circulating blood. They may also help with alertness by raising the level of the amino acid tyrosine in the blood and brain. Tyrosine is converted to hormones such as noradrenaline and dopamine, both of which make us feel energised, says Clark.

However, the link between food and afternoon energy levels is far from clear-cut, as many variables such as age and what you ate for the previous meal can influence the connection. Even your temperament can make a difference. 

Anxious types are less susceptible to a post-lunch dip in performance, and a high-carbohydrate snack can even help them feel and perform better, according to research conducted by Rob Markus, associate professor of neuropsychology and psychopharmacology at Maastricht University.

Put productive afternoons on the menu

What does this all mean for your daily lunch choice? If you do tend to struggle with the afternoon slump, it’s worth experimenting by swapping your high-GI white bread, pasta or rice-based lunch for one based on cooked or salad vegetables with a high-protein food such as meat, chicken, eggs, nuts or legumes, and healthy fats from avocado, nuts and olive oil.

Our response to food is highly individual, so let your body be the judge. As you test out different lunch choices, control as many other variables as you can by getting the same amount of sleep at night, eating the same thing for breakfast, having lunch at the same time and keeping caffeine intake constant. 

Fading fast? Give this a try

Keep an eye on GI

The glycaemic index (GI) ranks carbohydrate foods according to how they affect blood glucose levels. Carbohydrates with a low GI value (55 or less) are more slowly digested, absorbed and metabolised by your body and cause a smaller, slower rise in blood glucose levels and, therefore, insulin levels. Check the GI of your favourite lunch foods.

Snack to fuel your workout

Once out of the mid-afternoon slump, those heading for the gym after work can benefit from a late-afternoon, high-carbohydrate snack.

“A light snack a couple of hours before exercising, such as a piece of fruit or muesli bar, can help top up your muscle glycogen stores that will fuel your workout,” says sports dietitian Robbie Clark. However, there’s no need to load up on carbohydrates unless you’re an elite endurance athlete.

Working week nutrition basics 

  • Don’t skip lunch or let yourself get too hungry
  • Drink water regularly to keep your body hydrated
  • Eat small, frequent meals
  • Ensure your lunch includes generous amounts of vegetables and a moderate serve of a high-protein food
  • If you are eating carbohydrates, choose low-GI foods

Which tasks are most susceptible to the post-lunch slump?

Your performance on tasks needing sustained attention is more likely to be impaired by a high-GI lunch, according to a June 2002 paper in Nutrition Research Reviews.

Read next: What's so special about the 90-minute mark?


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