Two varieties of kiwifruit may help boost immune function and respond to infection, according to research published in the Proceedings of the nutrition Society of New Zealand.
Three studies were conducted which looked at the Gold kiwifruit and Green kiwifruit produced by Zespri Group, a New Zealand producer of the fruit. They found that these varieties of kiwifruit may:
- Enhance the body's natural immune response, allowing it to fight off colds, the flu and other illnesses 
- Reduce inflammation which is associated with long-term diseases such as arthritis, cancer, heart disease, diabetes and obesity 
- Assist in achieving the optimum balance between good and bad bacteria in the intestines 
- Protect against cancer associated enzymes in the lower digestive tract 
- Protect muscles against exercise-related oxidative stress 
These studies provide further evidence to support previous research on the kiwifruit's ability to support the body's natural defenses. In 2001, a leading nutrition scientist at the Rowett Research Institute showed that eating kiwifruit daily can protect DNA against damage that may lead to cancer. More significantly, kiwifruit was found to help repair the damage caused to DNA. 
The Zespri Green kiwi (Actinidia deliciosa) is commonly known as 'Hayward' and is the most popular and most consumed variety of kiwi. It has brown, furry skin and green flesh.
The Zespri Gold kiwi (Actinidia chinensis 'Hort16A') is a cross-bred variety which has yellow flesh.
The kiwifruit is the most nutrient-dense of the twenty-seven most commonly eaten fruits. It has more Vitamin C that any other fruit. Kiwis are high in fiber, potassium, and Vitamin E. They also contain lutein, the phytochemical that is associated with reducing the risk of cancer and heart disease.
-  Skinner MA et al health benefits of ZESPRI GOLD Kiwifruit: Effects on muscle performance, muscle fatigue and immune responses. Proceedings of the nutrition Society of New Zealand, 2008, Volume 32, pages 49-59.
-  Farr JM, Hurst SM, Skinner MA. Anti-inflammatory effects of kiwifruit. Proceedings of the nutrition Society of New Zealand, 2008, Volume 32, pages 20-25.
-  Molan AL, Kruger MC, Drummond LN. Kiwifruit: The ability to positively modulate key markers of gastrointestinal function. Proceedings of the nutrition Society of New Zealand, 2008, Volume 32, pages 66-71.
-  Collins BH et al kiwifruit protects against oxidative DNA damage in human cells and in vitro. Nutr cancer. 2001;(1):148-153.