RDC (Randomised Controlled Trial)

A clinical study where participants are randomly assigned to either an experimental group (receiving the intervention) or a control group (receiving a placebo or standard care).

Purpose: To minimise bias and establish causal relationships between interventions and outcomes.
Gold Standard: Considered the highest quality for testing effectiveness and safety of treatments.

What does it mean if there are no RCTs on a given topic?

The lack of RCTs on a nutrition topic does not mean there is no risk or no scientific basis for concern. While RCTs are considered the strongest form of evidence, they are not always possible in nutrition research for two main reasons:

1) Practical limits: Many health outcomes, like heart disease or cancer, take decades to develop. Running an RCT that controls participants’ diets for decades would be extremely expensive, difficult to enforce, and likely impossible to recruit for. Instead, it is much easier for scientists to rely on long-term cohort studies, which follow large groups of people over time.
2) Ethical limits: Researchers cannot knowingly expose people to harmful substances. For example, tobacco is a known carcinogen globally, and trans fats are now recognised as harmful to heart health and banned or restricted in many countries — even though no RCTs were conducted. It would be unethical to ask participants to smoke daily or eat trans fats for years in an experiment.

Because of these challenges, scientists use observational studies and apply frameworks like the Bradford Hill criteria to judge whether a food or nutrient is likely causing harm or benefit. These criteria look for things like: does the effect appear consistently in many studies, is it biologically plausible, does risk rise with higher exposure, and does removing the exposure reduce risk? When enough of these conditions are met, researchers can conclude there is a causal relationship — even without an RCT.