This section is from the book "The Hygienic System: Fasting And Sun Bathing", by Herbert M. Shelton. Also available from Amazon: The Hygienic System Vol III Fasting and Sun Bathing.
Some caution against eating during or immediately following a sunbath. I know of no reason for either rule. It will be noticed that the lower animals usually get their food and sunshine together and then retire to the shade to digest their meal. Rikli had his patients to go up early for their sun baths and either to eat while bathing or else to retire to the breakfast room immediately upon coming down from the mountains. I have seen no evidence of ill effects from eating during or immediately after sunbathing.
The best and healthiest rule in the sunbath is constant movement. Rest in the shade. Pigmentation is slower, but one is less likely to be injured if moving about than if lying still. However, the fact that one does not have an enclosure where activity is possible should not deter him or her from having a sun bath.