Half of secondaries serving deprived and statistically unhealthy areas are not even close to meeting new nutritional standards for lunches and other school food, Ofsted has found.
The watchdog visited a sample of schools in areas with low life expectancy and high rates of cancer and heart disease to see whether they had had introduced the new standards made mandatory last year.
They were designed to move schools away from unhealthy, processed food like "Turkey Twizzlers". But of the 16 secondaries, only half had complied or were close to complying with the lunch and other school standards.
They include restrictions on salt, saturated fat and other unhealthy elements with minimum content for necessities such as calcium, vitamins and iron.
Ofsted said: "The standards most often not met were those restricting the provision of meat products, deep-fried foods and starchy foods cooked in fat or oil. Generally, this resulted from misinterpretation of the standards rather than deliberate non-compliance."
Primaries, where the standards were introduced a year earlier in September 2008, did better with 15 out of 16 complying or close to complying.
Some heads were reluctant to speak to parents about unhealthy packed lunches in case they were seen as patronising.
Only ten of the 16 primaries had complied with standards for food other than lunches.