Globally, dietary problems can relate to either too little or too much. 

Obesity is primarily linked to excessive consumption of highly refined carbohydrates; it is not explicitly associated with meat or milk consumption. A high animal protein diet in fact provides more protein relative to calories and is potentially beneficial in achieving weight loss and a healthy lifestyle.

Conversely in societies with very low meat and milk consumption where people are  reliant on low-cost starchy root vegetables and grains, there can be severe malnutrition problems in children leading to stunting, ill health and compromised cognitive development.

Over-consumption of  processed, and carbohydrate-rich foods can not only lead to obesity it can also cause  the paradox of both extreme malnutrition and obesity within not only low- and middle-income countries  but also sometimes high-income populations as well.

Despite these evident dietary concerns, conducting reliable nutritional intervention studies presents significant challenges. The reasons include:

•        often the subjects or their diets cannot be controlled, 
•        most studies are too time-limited  to show a biological change (which may take years), 
•        a person’s diet consists of a multitude of inputs and changing one may not have the effect assumed.

However, there have still been some credible  well controlled and valid biological investigations that have yielded valuable insights into the role of certain foods or food components on health and disease.

Most nutritional information relating to disease conditions is derived from observational (epidemiological) studies. However, these are correlational in nature and can only suggest hypotheses that require more rigorous biological examination. They cannot in themselves establish causation.

The WHO and the Australian NHMRC recommend use of GRADE procedures when conducting meta-analysis of nutrition and pharmaceutical studies. The GRADE procedures weight contributing studies based on the design and standard of contributing research, placing a high weighting on well-designed randomised control studies and low weights on observational studies.

Much of the widely quoted research on diet and nutrition has been based on these observational studies, where the conclusions reached have been accepted as factual evidence of cause and effect, by the general public and in some cases even by scientists who may not have exercised appropriate professional scepticism.

Analysis utilising the GRADE methodology has found that most reported theories of  negative relationships between red meat and dairy consumption and human health have come from observational studies, which themselves show low Relative Risk ratios.

Follow up with clinical trials seldom shows a clear cause and effect relationship between red meat and dairy and specific disease conditions.

Follow this link below to see the conclusions of recent high-quality reviews that concluded there is little to low certainty evidence to support red meat causes diabetes, heart disease and cancer.