Carb to Fibre Ratio
Author Nina Evans, Research & Trainer in Public Health/25 April 2019
Checked and edited by Dr Sean Wheatley, Science and Research Lead/21 July 2026
Independently, both low carbohydrate and high(er) fibre diets have been shown to be beneficial for people living with Type 2 diabetes. It has therefore been suggested that a dietary approach which combines the two will have additional benefits. It has even been suggested that it is increasing intakes of refined carbohydrate, alongside decreasing intakes of fibre, which best explains the increase in the prevalence of Type 2 diabetes over the 20th century. These two factors can be considered together, using the “carbohydrate to fibre ratio”.
This blog will discuss what the carbohydrate to fibre ratio is, who is using it, and whether we should be too.
Carbohydrates
Before we delve into the pros and cons of the ratio, let’s start off with some definitions. Carbohydrate is one of the three main macronutrients, alongside fat and protein. It is the only nutrient which directly influences blood glucose levels. There are two types of carbohydrate that provide dietary energy; sugars and starch.
Fibre
Dietary fibre is also a type of carbohydrate. It is almost exclusively plant-based. Unlike starches and sugars, fibre is not digested in the small intestine, and is often referred to as “indigestible carbohydrate”. It is recommended that we all have approximately 30g fibre per day. Many of us get less than this though, which the current average intake being about 18g. High fibre foods are defined as those which have over 6g fibre per 100g of the product.
Carb to Fibre Ratio
The carbohydrate (carb) to fibre ratio is easy to calculate. Simply divide the total carbohydrate of the food or drink (in grams) by the fibre content (in grams).
The lower the ratio the better, as lower values show that the food is lower in carbohydrate and/or higher in fibre. Both of these things have previously been shown to be beneficial for the management of type 2 diabetes. This is because there is less carbohydrate for the body to have to deal with, and/or the carbohydrate that the food contains is absorbed more slowly (making it easier for the body to deal with). Blood glucose and insulin spikes are reduced as a result.
One of the main advantages of using the carbohydrate to fibre ratio, rather than other classifications (such as glycaemic index), is its simplicity. It can be identified with an easy calculation, and it can be worked out using food labels alone, without the need for any other reference materials or sources of information.
“Net” Carbs
It is noting that there is one key difference in how this ratio is calculated depending on where you are. In the United States, for example, the carbohydrate value on food labels includes fibre. The fibre therefore needs taking away from this value (to work out “net carbs”) before the carb to fibre ratio is calculated. In the UK though, the carbohydrate values on nutrition labels have already had the fibre substracted from them, so the carbohydrate and fibre values on the label can be used to calculate the carb to fibre ratio stratight away.
What is a “good” ratio?
Recent(ish) research from the Harvard School of Public Health, based on the American Heart Association 2020 Impact Goals, concluded that a product should ideally have at least one gram of fibre for every 10 grams of total carbohydrate (i.e., should have a carb to fibre ration of 10) to be considered a healthy-promoting option. This is based on the carb to fibre ratio of a whole, unprocessed wheat grain.
Others have suggest that the “ideal” ratio for carbohydrate to fibre should be closer to 5, though there seems to be limited evidence for this.
What does the research say?
Initial research by Gross et al. (2004) suggested that the increase in carbohydrate and decrease in fibre over the past forty years is associated with the Type 2 diabetes epidemic in the United States. After this association was highlighted, further research has looked into the carbohydrate to fibre ratio.
The carb to fibtre ratio is sometimes used to help consumers identify products which are based on refined carbohydrates (and which are heavily processed). After evaluating 545 grain-based products in the US, the Harvard School of Public Health found that foods with a ratio of 10 or less also tended to have less sugar and trans fats than those which didn’t.
Another small (n=164) cross-sectional study suggested that the carbohydrate to fibre ratio is closely associated with various clinical markers. These include triglycerides, high-density lipoprotein cholesterol, and the presence of the metabolic syndrome. Further cross-sectional research suggested that a diet with a lower carbohydrate to fibre ratio was associated with significantly lower mean body weight. It was also linked with having lower mean fasting serum insulin levels, insulin resistance and HbA1c (a measure of blood glucose control).
So, overall, research suggests that the carbohydrate to fibre ratio may be associated with some benefits.
Limitations
It is however important to note that mostof the research looking at the carb to fibre ratio has been observational, which can not show if there is a causal relationship (i.e., it can not be used to prove that eating foods with a lower carb to fibre ratio caused the health improvements that were observed).
As well as this, these studies all used food frequency questionnaires (FFQ) to assess participants’ diets. This is another major limitation, as this method often fails to provide a valid measurement of what people are actually eating. The confidence we can have in the outcomes of these studies is therefore reduced.
What about other carbs?
Another possible limitation of the carb to fibre ratio is that much of the current research focuses on grains, and not other sources of carbohydrate (e.g., from fruits, vegetables or dairy products). It is therefore questionable as to whether these findings truly apply to all carbohydrates.
If we use fruit as an example, the ratio does still seems to provide a relatively good indication of which types might be a better choice for someone with type 2 diabetes though. For example, a banana has a carbohydrate to fibre ratio of 15.3 (total carbohydrate 20g per 100g + fibre 1.4g = 21.4/1.4 = 15.3). This does not meet the 10:1 or 5:1 ratio or classification of a food high in fibre. Raspberries, on the other hand, have a ratio of 1.7 (total carbohydrate 4.6g per 100g + fibre 6.7g = 11.3/6.7 = 1.7). So although further research is perhaps needed, we shouldn’t necessarily write off its benefits when considering other foods.
Conclusion
The carbohydrate to fibre ratio is simple to work out, and may, in theory, provide a good indication of which foods are more or less likely to be a good choice for someone living with type 2 diabetes. There are however question marks over what the ideal ratio might be, and exisiting research using this marker has important limitations.
For further information on ranking systems for carbohydrates, read our blog on glycaemic index and glycaemic load. You can access it here.
