Does one size of diet fit all? Is there a universally healthy diet? 

Recent large-scale studies have shown that people have profoundly individual responses to the same food. The results of these and further studies will mean that individualised diets can be formulated for health and weight management – a concept called Precision Nutrition. The individual nature of metabolic response is likely to be the case in our pet species too. So, these advances will impact us as pet owners leading to better informed, specific feeding for our pets.  

Tim Spector and his team at King’s College, London have published studies that look at these idiosyncratic reactions to food (1,2). The studies concentrate on two parameters, glucose (sugar) and fat, looking at their levels in the bloodstream after eating. Large spikes in blood glucose after a meal are known to increase the possibility of diabetes, heart disease and obesity. Obesity itself is related to many other health conditions. Similarly, large increases in the level of fat can cause inflammation and disease. Triglycerides are the fats most often studied. 

The Glycaemic Index Problem

For many years we have considered the idea of every food having a glycaemic index. This suggested that foods are digested at a certain speed and release glucose into the bloodstream quickly or slowly. Foods were classified as low or high glycaemic index. Low glycaemic index foods were thought to be broken down slowly and reduce blood glucose spikes. These foods were recommended for health and weight management. However, Spector and his team found that the glycaemic index of food is not a constant and shows huge variation in individuals. 

Scientists at the Weizmann Institute of Science in Israel published a paper comparing glucose spikes when people ate white bread or sourdough bread. They claimed the latter was ‘the best bread money could buy in Tel Aviv’. The expectation was that the sourdough bread would cause lower blood glucose levels than the white bread. The results showed that this was not true, people showed very different responses. The same happened with beer, ice cream and vegetables. 

All the studies measured biometric parameters in their subjects, parameters such as body mass index, waist to hip ratio and age. The scientists also assessed the types of bacteria in the gut (microbiome) by looking at DNA in stool samples. Data was also collected on physical activity, rest and sleep, as well medical history. The inclusion of identical twins in some of the studies has allowed assessment of the effect of genetics. 

Genetics – can we predict response to food?

The results of the studies show that genetics play a small part in our metabolic response to food. No genetic effect was seen on fat metabolism. A 30% genetic effect was found on sugar metabolism. The important parameters were found to be the gut microbiome, physical activity and sleep. Responses to food were also affected by the time of day the food was eaten as well as baseline sugar, fat and insulin levels. 

The microbiome

The gut microbiome has been studied in humans for some time. The number of bacteria in the gut outnumber our own cells and have a huge effect on our health. The bacteria themselves produce metabolites. These metabolites play important roles in our bodies and those of our pets. 


The term “dysbiosis” refers to imbalance in the gut flora, the normal population of microbes. Dysbiosis is known to be associated with psychiatric and neurological illness in humans. It seems impossible but some of the metabolites produced by the microbiome are used to transmit messages within the nervous system. Tryptophan is a neurotransmitter that is formed by the microbiome. Some metabolites seem to contribute to the formation of cancer, some prevent it. For example, in humans colo-rectal cancer is associated with dysbiosis. 

What about in dogs?

It is early days for the study of the microbiome in the dog. A laboratory in Texas does offer a dysbiosis index. This looks at the bacterial DNA in fresh faeces to assess 8-9 species. Studies have shown that gastrointestinal disease results in a reduction in the diversity of the microbiome. Some types of bacteria are present in reduced numbers and other bacterial forms increase. It is not yet known whether this is the cause or effect of disease.  Similar changes are seen in metabolic diseases such as diabetes and further studies will show if management of the microbiome can impact such diseases. 

So how is this useful?

A greater understanding of the microbiome will feed into research on precise nutrition for animals. In humans, analysis of the microbiome can be used to predict response to chemotherapy. Therefore, measures are taken to manage the gut microbes before chemotherapy starts in some patients. We may find that the same is true in animals that manipulating the microbiome can help to treat and manage disease. 

Researchers are developing blood, urine and faecal tests in humans to predict metabolic response. This will inform the development of individually designed diet plans. The U.S National Institute for Health is looking at delivering diets in this way.

Ultimately, this science will be applied to dogs. This will allow us to feed according to their individual responses to certain ingredients. Anyone who has attempted to diet their dog will know how difficult it can be. Perhaps this new knowledge explains why weight management diets don’t work for every patient! This does not explode the fact that calories in should equal calories out to maintain health but it will allow us to minimise sugar and fat spikes in the future. In this way we can reduce the health threats of obesity, diabetes, pancreatitis and liver disease

Precision nutrition is an interesting area of research which may give us great confidence in the diets we feed to our pets in the future.   

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  1. Berry S, Valdes A, Davies R, Delahanty L, Drew D, Chan AT, Segata N, Franks P and Spector T. Predicting personal metabolic responses to food using multi-omics machine learning in over 1000 twins and singletons from the UK and US: The Predict study (OR31-01-19) . Current developments in Nutrition. 3 (1). 
  2. Matey-Hernandez ML, Williams FMK, Potter T, Valdes AM, Spector TD and Menni C. Genetic and microbiome influence on lipid metabolism and dyslipidaemia. Physiological Genomics 2017. 50 (2):117-126