Fasting

[Updated March 15, 2015] The AICR/WCRF report on nutrition and cancer does point out that "Restriction of energy intake from food is the most effective single intervention for preventing cancer in experimental animals."
[link]

Unfortunately, the evidence for the anti-cancer effet of fasting is mostly based on animal studies or in human studies with significant limitations. Furthermore, not all the evidence is positive and there have been some negative results such as this study which found no benefit to fasting twice a week in mice injected with prostate cancer cells:
[PMID: 20733612]

Dr. Yu offers the opinion that fasting may be more useful in conjunction with other methods than by itself. [Youtube video]

A survey paper on fasting and cancer in animal studies is available here: [PMC4263749].

Some ways fasting might be carried out are:

- continuous calorie restriction.  Reduce the number of calories eaten each day.

- daily intermittent fasting.  Only eat within a prescribed time window every
  day.  This diet is described in the Fast 5 diet on the [Fast 5 web site] and
  in the free downloadable ebook on that site. It discusses fasting for 19
  continuous hours and eating only within the remaining 5 hours each day.
  [Fast 5 web site]
  [Fast 5 ebook]
  [Fast 5 discussion]
A recent experiment on fruit flies supports this idea finding that fruit flies who were restricted to eat within a 12 hour window each day had superior cardiac health than fruit flies allowed to eat any time they wished. See [PMID: 25766238] and [San Diego University news release].
- Alternate Day Fasting.  Every other day reduce calories to 25% of normal.

- weekly intermittent fasting.  On the 5:2 diet one eats normally 5
  days a week and reduces calories to 25% of normal on 2 non-consecutive
  days a week.  The diet is described in the book Michael Mosley, The Fast
  Diet: Lose Weight, Stay Healthy, and Live Longer.

- monthly intermittent fasting.  Dr. Vatter Longo has been experimenting
  on humans with a diet in which one eats normally for 25 days and then
  reduce calories to 25% of normal for 5 days.  (It has also been
  hypothesized that eating normally for 55 day and reducing calories
  to 25% for 5 days might be give the same benefit.)
  [BBC News]
  [Valter Longo - Wikipedia]

Note that many of these diets have been considered only from the viewpoint of weight loss and not from the viewpont of any potential anti-cancer effect.

The area where some evidence is available is that human studies have found that fasting before and after chemotherapy seems to heighten the anti-cancer effect and reduces adverse side effets.
[PDF]

Many of the mechanisms underlying fasting are known. The following
survey paper is aimed at fasting and chemotherapy but it also describes,
in general, the various biological mechanisms underlying fasting:
[PDF]