The study cited by Ceejayoz contains the following statement:
Ramadan fasting is similar to ADF [alternate-day fasting], because both fasts incorporate feast periods and fast periods.
Since 2010 when that study was published there has been new positive research on ADF.
Maideen, Pakkir, et al."Adverse health effects associated with Islamic fasting: A literature review." Journal of Fasting and Health 5.3 (2017): 113-118.
Animal studies have suggested that ADF is likely to increase lifespan (6) and prevent cardiovascular diseases (7, 8), diabetes (9), kidney disease (10), neurodegeneration (9), and cancer (11).
(The above citations are all about ADF, not about Ramadan fasting)
Islamic fasting is a healthy, nonpharmacological
approach for health improvement,
which is associated with numerous
health benefits, including weight loss (12, 13),
reduced inflammation (14), improved insulin
sensitivity (15), detoxification (16), elevated
endorphin levels (17), immune cell regeneration
(18), and overcoming addictions (19).
Furthermore, Islamic fasting has been shown to
reduce hypertension (10), asthma (20), and
rheumatoid arthritis (21).
The article also finds that Ramadan fasting is bad for diabetics (who are not encouraged to fast in Islam), or if people rush to eat fatty or greasy foods at the end of the day.
But this literature review is from a fairly minor journal in an Islamic country, written by Muslim scientists. The "detoxification" citation makes the review particularly suspicious as it cites a completely pseudoscientific self-published book. I don't think this review applied scientific levels of skepticism, even if the other studies it cites look more respectable.
Here's a more technical, careful literature review from an Islamic country:
"The effect of Ramadan fasting on cardiometabolic risk factors and anthropometrics parameters: A systematic review" Pak J Med Sci. 2015 Sep-Oct; 31(5): 1250–1255.
Ramadan fasting is associated with elevations in high-density lipoprotein cholesterol (HDL-c), and reductions in low-density lipoprotein cholesterol (LDL-c) and total cholesterol (T-chol). However, the lipid profile of diabetic patients deteriorated significantly during Ramadan fasting. In addition, Ramadan fasting lowers body weight, body fat percentage and BMI (body mass index). However, the relationship between weight reduction and loss of body fat is not studied. The majority of patients with stable cardiac illness can opt for Ramadan fasting safely. However, the long term effects of Ramadan fasting on cardiovascular outcomes and risk factors remains uncertain, and the apparent discordant effects in individuals with and without diabetes mellitus merits further study.
And another, this time from an American journal:
"Is Ramadan fasting related to health outcomes? A review on the related evidence" J Res Med Sci. 2014 Oct; 19(10): 987–992.
Studies reported that Ramadan fasting may decrease the concentration of IL-6, IL-1β, TNF-α and number of leukocytes and monocytes. Elevated concentration of proinflammatory cytokines (e.g., IL-6, IL-1β and TNF-α) is known as a risk factor for cardiovascular diseases,[42,43] insulin resistance and cancers. Suggested mechanism is that Ramadan fasting results in oxidative stress reduction, and therefore, lower level of reactive oxygen species. On the other hand, body fat decreased during Ramadan in this study, and therefore, proinflammatory cytokines secretion would be decreased.
Here is a medical flyer explaining this health outcome in relatively simpler language, as well as discussing the risks associated with Ramadan for diabetics.
Fasting in general is associated with reduced risk of cancer and better treatment of cancer, but there is little research that has looked at Ramadan in particular, as this study shows:
"Ramadan Fasting and Patients with Cancer: State-of-the-Art and Future Prospects" Front. Oncol., February 2016
The effects of fasting on cancer have been extensively studied: starvation-induced changes in genome organization, chromatin remodeling, and metabolic pathways modulating, for example, glucose, insulin-growth factor (IGF), and other related enzymes and proteins may increase the effectiveness of chemotherapy (30–32). Fasting has an anti-Warburg effect and could have a positive impact on drug pharmacokinetics and could contribute to reduce its side effects, improve the chemotherapeutic index, and overcome at least partially the issue of drug resistance (30–32). Furthermore, fasting has a beneficial impact on the renewal of stem cells and on the immune system, in particular on natural killer cells, as well as on the oxidant system, thus enabling cancer growth control (33–36). To this respect, different kinds of cancer have been investigated, such as pancreatic (37), breast (38–40), lung (41), colorectal (42) and prostate (43) cancer, and even glioma (44). The impact of fasting has been assessed on different drugs (45, 46), including irinotecan (47, 48), doxorubicin (49), and on new recent anti-blastics, such as erlotinib (41), tyrosine kinase inhibitors (50), and sirtuin (51), among others.
Effects of fasting on tumor have been assessed both on neo-adjuvant and adjuvant therapy (40). Furthermore, fasting seems to sensitize tumor cells and increase the outcome of radiation therapy (44).
However, despite that this topic has attracted an impressive body of research (52, 53), little is known both in terms of molecular mechanisms and clinical outcomes about the difference among the various existing kinds of fasting, such as periodic diet (54), calories restriction (55), dietary restriction (56) or dietary manipulation (53), intermittent (38, 43, 57) or short-term fasting (40, 49), and prolonged fasting (33, 35, 39), among others. Lv and collaborators in a recently published systematic review and meta-analysis concluded that while the roles of ketogenic diet and of caloric restriction in controlling cancer are quite established, evidence of the effectiveness of intermittent fasting is still insufficient (57). Furthermore, most of these studies have been conducted in animal models; therefore, there is an urgent need for more investigations in human (58).
This study found no consensus on the effects of Ramadan fasting in particular on cancer.