Instead of lollies and high sodium foods to snack on, Miss Russell advised students to eat fruit, raw nuts, low-fat yoghurt and crackers with hummus.
Water should be the only drink during study time and it's important to stay hydrated as dehydration can reduce cognitive abilities, Miss Russell said. Alcohol should be avoided as it dehydrates the body.
It's also important to get into a routine of eating a healthy breakfast as it gives the brain the best possible start to the day, and meals should not be skipped.
"Breakfast gives the brain fuel to be able to start working effectively, especially after the fast your body has been in overnight. Wholegrain toast and eggs, banana smoothie, or high-fibre cereal with fruit and milk."
Last year, there were about 40,000 tertiary students in New Zealand and in July last year there were 286,886 secondary students.
University students have already started sitting their exams and high school students are due to start their NCEA examinations on November 9.
Students needed to try to get a good night's sleep, take regular breaks and get outside for fresh air to help bring back concentration, which we tend to lose during the mid-afternoon, Miss Russell said.
The New Zealand Federation of Family Budgeting Services chief executive Raewyn Fox said the catch in eating well was that it could seem more expensive, especially for students living on little income.
Ms Fox said the secret was planning.
"Try to bulk buy with your friends and get some nice, healthy vegetables and fruit, some meat and cheese, so you can make stuff up yourself, which isn't easy. If you're studying for exams, time is an issue as well."
It also paid to shop around because some places were cheaper than others for certain types of food, Ms Fox said.
Markets were a good place to get fresh produce because it was cheaper there than at the supermarket.
Ms Fox said one of the issues that students found especially hard was that they were usually forced to live week-by-week because their incomes are from a part-time job or student allowance.
"Look at what you're spending and see if it's all essential - what you don't need, cut so you can afford to buy those healthy foods," she said.
Good diet helps keep doc away
Joe Tiddy doesn't have the typical diet of a student.
The 26-year-old, who is studying graphic design in Auckland and is working long hours to complete his end-of-year portfolio, avoids two-minute noodles and toast.
The Media Design School student tries to take a healthy lunch every day, opting for meat and fresh broccoli and carrots which he steams at the school communal kitchen.
If he hasn't packed a lunch, his takeaway of choice is a chicken sandwich on honey oat bread with lettuce, tomato, pickles, olives, and jalapenos from Subway. Although he admits to adding cookies to his order.
Mr Tiddy says he doesn't always adhere to this healthy diet as specials for junk food snacks can become too hard to resist, and he treats himself on occasion.
He hasn't been sick this year and believes his healthy diet is to thank for that.
"I'm definitely prone to biscuits ... last Friday I had some KFC."
Many of his classmates consume several energy drinks during the day, but Mr Tiddy fills up his water bottle at the tap. Fruit is also another favourite on his shopping list.
"Oranges, love them in season ... bananas, pears, grapes as well ... I just buy them in season," he said.
Breakfast is usually frozen berries or three cooked eggs and dinner is usually a meat and vegetable dish.
