You're barely a third of the way through your working day and already your energy is sapped, your concentration has gone out the window and you can feel a headache coming on.

It's an all too familiar scenario for thousands of Irish workers, but it is something that can easily be radically changed -- by including some exercise in your day and eating more healthily.

Nutritionist and personal trainer Kellie Collins says eating well can really pay off in better results at work.

"Eating high Gi (high-sugar, low-fibre) foods such as pastries will cause sharp increases and decreases in blood sugar levels, which means you will be hungry soon after eating these foods and this will affect your concentration," she says.

"Being hungry means you will be thinking about your stomach and what you are going to eat next, rather than concentrating on your work."

While some companies provide healthy food in a canteen or have a kitchen in the building, it's often the case that workers have to buy sandwiches or pop out to pick something up at the local shop.

"It's really all about being prepared," says Dr Muireann Cullen, manager of the Nutrition and Health Foundation (NHF), which organises the 'Workplace Wellbeing Campaign'.

"One great idea is to cook a couple of meals in advance of the working week and bring in portions for lunch every day.

"It's really essential that people try to take a proper lunch break and they should actually leave their desk while they eat their meal."

It may take a while to change the habits of a lifetime, but making sure you have breakfast every day and ditching the mid-morning pastry treat will soon start to pay dividends.

We asked three people with different working routines to share their food diaries with us and also asked nutritionist Kellie Collins for her top food tips to see you through the working day.

The early riser: and her 6am breakfast

Sharon Tobin is a news presenter and reporter with TV3. It's an early start for Sharon when she presents the morning news on Ireland AM.

"I usually get up around 3.15am and get into work for 4am," she says. "I have a coffee and then I have some breakfast around 6am. I'm usually quite good at making sure I eat breakfast -- it's often a bowl of granola or muesli with some fruit and yoghurt."

It's usually around noon by the time she leaves work.

"I know that should be my dinnertime but I'm not hungry for a big meal," she says.

"I usually grab a sandwich or a wrap. I normally have my dinner at 6.30 or 7pm.

"I know that's quite close to my bedtime, which is around 8pm, but I usually like to wait to have dinner with my fiancé."

Dinner usually consists of lots of vegetables along with fish. "We both like cooking so we usually make meals from scratch rather than having takeaways or ready meals."

This eating routine changes when Sharon is on reporting shifts rather than the early news-presenting shift.

"If I'm out on the road reporting then it's often a case of grabbing a sandwich or something from a garage," she says.

"I'm much more organised when I'm working early."

Kellie's comments

"I'm delighted to see that Sharon makes time for a healthy breakfast soon after she starts work.

"It's a long time from 6am to lunchtime, so it would be good for Sharon to have a snack mid-morning -- a piece of fruit, a yoghurt or a small handful of unsalted nuts and some dried fruit would be good options. Sharon should also try to have a snack in the afternoon -- perhaps some wholegrain crackers with cheese or hummus.

"It's great that Sharon and her fiancé like cooking from scratch -- it's a fantastic opportunity to experiment with herbs and spices, rather than turning to convenience foods that are often high in salt."

The businessman He's a smoothie

Diarmuid Crowley is a co-owner of Wild Orchard smoothie company. He lives in Adare, Co Limerick.

It comes as little surprise that Diarmuid starts his day with a smoothie -- one made with natural pro-biotic yoghurt and fruit. He follows this up with four Weetabix with milk poured on top.

At around 11am, he eats a piece of fruit, such as a banana or an apple.

"At lunchtime, I usually have a couple of ham and cheese sandwiches. I make them up myself with brown bread, butter, ham and cheese. Sometimes I might have a tuna sandwich but I usually stick to the same thing.

"I usually don't stop to take a formal lunch hour. It's more a case of sitting at my computer and eating my sandwiches."

As part of his lunch, he usually has an apple and drinks a coffee.

"Usually at around 3pm, I'll have another smoothie. Then I'll have another coffee at about 4pm."

Diarmuid and his wife take turns to cook dinner for the family. "I'll usually make something fairly straightforward like mashed potato, pork chops and so on. My wife would be better at making meals like chilli con carne or chicken kebabs."

Kellie's comments

"Diarmuid's diet seems very well-balanced and he eats regularly throughout the day, which is great for keeping his energy levels up.

"Smoothies are a great way to boost fruit intake, and the yoghurt in the smoothie will contribute to his daily calcium intake.

"Eating sandwiches for lunch is absolutely fine, especially since Diarmuid is organised enough to make them himself, so he knows exactly what's in them.

"Diarmuid could perhaps vary his sandwich fillings during the week -- lean ham or tuna are good choices, but turkey, chopped grilled chicken or tinned salmon would also be suitable fillings.

"A little salad in the sandwich will help to boost his daily vegetable intake.

"Finally, Diarmuid doesn't mention his water intake -- he should aim for two litres per day -- keeping water on his desk and in the car will help him to achieve this."

The working mother: water way to go

Sian Gray is head of marketing for Nokia Ireland.

“I usually get up at 6.15 in the morning and have an Actimel at home before I drop my daughter Mia to the crèche,” she says.

“I have a bio-fruit yoghurt when I get to work. I also get through about three small bottles of water during the day.”

When it comes to lunchtime, Sian prefers salads to sandwiches.

“I’m not that fond of bread so I usually have something like a chicken salad with lettuce, tomato, cheese and olives along with a bit of balsamic dressing. I’d often have a fruit salad afterwards.”

Sian usually stocks up on food for work at the start of the week.

“On a Monday, I’ll head to the shop or to Donnybrook Fair to buy food to last me during the working week.”

When the dreaded midafternoon slump hits, Sian snacks on apricots, raisins and cashew nuts.

“If I’m going to the gym later on, I’ll eat my dinner around 5.15. Otherwise, I’ll wait until my husband comes home from work.

“I can’t head off to exercise without having something to eat first. I try to keep away from stodge so I’ll eat something like noodles or a chicken stir fry with lots of vegetables.”

Sian says that since becoming a mother, she eats more healthily.

“I used to have erratic eating habits – just grabbing something to eat when I could and sometimes skipping breakfast. But having a baby definitely makes you more aware of good nutrition.”

Kellie’s comments

“Sian is on the go all day so it’s essential that she has a good breakfast to set her up.

Yoghurt is a good option for breakfast, but it’s not really sufficient by itself, so I would recommend that Sian also introduce some wholegrain carbohydrates such as a wholegrain breakfast cereal or some toast.

“Sian should also try to have a snack mid-morning – again a piece of fruit would be good here.

“Her lunch choice is excellent – full of colour, which means it’s rich in immuneboosting vitamins and minerals.

“Sian is right to have something to eat before her workout – exercising on an empty stomach is not a good idea as it will ultimately affect your performance during the workout, and might even lead to overeating later in the day.”

Make your diet work

Breakfast

Thumbs Up:

Porridge; no-added sugar oat-based muesli with milk; toast made with nutty or seeded bread; fruit salad with yoghurt

Thumbs Down:

Breakfast rolls; sugar-coated breakfast cereal

Lunch

"There is a belief that eating carbs may cause you to be less alert, but for many people, carbohydrates form the main part of their lunch, for example by eating a sandwich, or a pasta salad or even a main meal with potatoes," says Kellie. To avoid feeling sluggish, she advises choosing low Gi, high fibre carbohydrates.

Thumbs Up:

Wholegrain bread; brown or basmati rice; baby boiled potatoes

Thumbs Down:

White bread; skipping lunch completely

Dinner

Thumbs Up:

Stir-fries; filling your plate with half vegetables, one quarter protein and one quarter carbs; lean chicken, turkey, red meat and fish are good meat options

Thumbs Down:

Limit your number of takeaways and processed foods

Snacks

Thumbs Up:

Two litres (eight 200ml glasses) of water a day; handful of unsalted nuts; fruit; yoghurt

Thumbs Down:

Chocolate; crisps; fizzy drinks

- Lisa Jewell