More fruit, less juice

Type 2 diabetes has become a major health issue in Australia where more than 1 million adults had been diagnosed with diabetes in 2010, with a projection for 1.5 million by 2030. In the US the problem is much worse, but as happens with so many phenomena, the rest of the world is following not far behind. For US adults older than 19 years of age in 2005-2006, the total incidence of diabetes (diagnosed, undiagnosed and pre-diabetes) was 42.3% and for those over 64 it was 72%! As many as 80% of patients with type 2 diabetes will develop and possibly die of macro-vascular disease. This results in major loss of life expectancy and quality of life, and medical expenses and lost productivity in the US were estimated to cost US$174 billion in 2007.

The main drivers of these alarming statistics and outcomes are obesity, populations living longer than in the past with increased likelihood of development of chronic diseases, and urbanisation leading to more sedentary activities. The first and third factors are modifiable by lifestyle changes, and one of the best ways to minimise the onset of overweight/obesity is through smarter dietary habits. Fruit and vegetable substitution for more nutrient-empty but high-calorie foods has been documented as an effective strategy to combat weight increases in numerous studies over many years. With the ready availability of all sorts of handy kitchen appliances nowadays, juicing fresh fruit has become a popular means of meeting fruit intake for many people. But does this affect their nutritional and health qualities compared to eating the fresh fruit whole? The following paper investigated this question and found while whole fruit had the expected beneficial result, juice significantly increased the incidence of diabetes (Diabetes Care (2008) 31:1311–1317).

The purpose of this study was to examine the association between fruit, vegetables and fruit juice intake and development of type 2 diabetes. A total of 71,346 female nurses aged 38–63 years who were free of cardiovascular disease, cancer, and diabetes in 1984 were followed for 18 years, and dietary information was collected using a semi-quantitative food frequency questionnaire (FFQ) every 4 years. The FFQ contained 16 questions on fruit consumption, 28 on vegetables and 3 on potato consumption which was a separate category. Median intakes of fruit, vegetables and juice for the bottom and top 20% were 0.5 and 2.5, 1.5 and 5.2, and 0.2 and 0.7 servings/day respectively. Diagnosis of diabetes was self-reported and then confirmed using standard diagnostic criteria. During follow-up, 4,529 cases of diabetes were documented, and the cumulative incidence of diabetes was 7.4%. In the statistical analysis of the data, allowance was made for the possible confounders of body mass index, family history of diabetes, smoking, post-menopausal hormone use, alcohol intake, physical activity and others that have been related to diabetes. It was found that an increase of three servings/day in whole fruit consumption was associated with an 18% lower hazard of diabetes. An increase of 1 serving/day in green leafy vegetable consumption was associated with a 9% lower hazard of diabetes, whereas the same change in fruit juice intake was associated with an 18% increased hazard of diabetes.

Some considerations that may have led to this unfavourable finding for juices are the following:

Many juicers separate solid material from the juice, so losing almost all fibre content of the whole fruit. This means soluble fruit pulp sugars are much more readily absorbed, leading to faster, higher blood glucose levels and subsequent major insulin release. In the whole fruit these sugars must first be released from the food matrix before they can be absorbed, resulting in the preferred slower and lower glucose peaks.
The solid materials in fruits are usually not as sweet as the liquids, so when the two are separated the resulting juice is much sweeter than when eaten whole and can lead to over-consumption. Similarly, drinking a prepared product can be much faster and more extensive than the alternative of having to cut, skin, chew and avoid seeds etc when eating the whole fruit. Although fruit juices are derived from healthy foods and are much better nutritionally than sugared beverages, when separated from fibrous material they can nevertheless be high in calories.
Juices don’t satiate as well as solid foods, so over-consumption can easily occur.
Valuable nutritional components of fruit may be kept separate from lytic enzymes in their whole form, but when cells are broken and disrupted with the juicing process these may then come in contact and result in loss or conversion of healthy nutrients. In addition to enzymatic action there may also be oxidative degradation as nutrients once released from the food matrix may be exposed to air. To minimise these losses, juices usually have to be consumed as soon as they’re prepared.

The moral of the story is to eat the whole fruit if and when you can.