Viral diets have a nasty tendency to combine two of my least favourite things: deprivation and maths. First there was the 5:2 diet (eat normally for five days, fast for two). The 40-30-30 “zone” diet (40 per cent of your calories from carbs, 30 per cent from protein and 30 per cent from fat) and the 16:8 rule (eat within an eight hour window, fast the rest). Now, it’s all about a new ratio – 30:30:30.