"One of the most highly researched fat burners is green tea," Hay told Healthista.
"Scientific studies show that drinking up to five cups of green tea a day can increase daily metabolism."
Matcha, the powdered version of green tea, has been proven in numerous studies to benefit the metabolism and significantly improve health.
2. Yerba mate
"Yerba mate works on hormone levels and blood sugar to help balance out cravings and studies have shown it could have an anti-obesity effect," says Hay.
It was also found to reduce levels of leptin, also known as "the obesity hormone" that sends hunger signals through the body.
"When it comes to metabolism and weight loss, yerba mate is extremely beneficial," says Hay.
3. Green coffee extract
Green coffee extract, the unroasted extract from the coffee plant, has been proven to help the body absorb glucose into the intestine.
Chlorogenic acid, found in green coffee, was found in studies to produce weight loss effects.
However, the process of roasting coffee removes the acid, so increasing your regular coffee intake won't have the same effect.
4. Black pepper fruit
"Black pepper fruit is a thermogenic spice which means it helps heat the body to burn fat and can also assist with the absorption of other nutrients," says Hay.
In 2011, a study found that mice fed a diet high in fats were still able to lose weight when given supplements containing black pepper.
5. White kidney beans
"There's a lot of research coming out about the fact that white kidney beans block carbohydrate absorption," says Hay.
The Journal of Applied Research published a study that found taking a supplement containing white bean extract 15 minutes before eating a meal can help reduce weight and waist circumference.
6. Maca
Maca, a native Peruvian vegetable, has been shown to improve endurance, helpful to dieters who are also working out to support their weight loss efforts.
One study showed Maca could also increase a person's sexual desire, improve performance of male cyclists and reduced weight gain in post-menopausal women.
7. Beetroot
Beetroot has been proven to be an athletic performance enhancer, used by Olympians pre-and-post exercise.
It is said to enhance muscle recovery due to Its high nitrate content.
The effects of beetroot juice were studied at the University of Exeter in Britain, where it was found that athletes' muscles worked more efficiently when using the supplement.
8. Cherry
Research suggests that cherry juice can help reduce fat around the abdomen.
A study in the Journal of Medicinal Food found tart cherries reduce body fat, especially in the belly when tested on a group of rats.
9. Baobab
Baobab is a super fruit typically found in Africa. It contains three times as much Vitamin C as an orange.
As well as helping strengthen hair, skin, and nails, Vitamin C is also vital in immune function - essential if you are working out often.
Scientists at the Oxford Brookes University Functional Food Centre also found baobab can help keep blood sugar levels stable.
Read more: • Ten ingredients healthy people have in their kitchens