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Protein - too much of a good thing? - December 2008
Everyone is concerned that so many children seem to be fat. Blame has been placed on almost everyone. You would think that nutritionists are the only ones who know how to get us out of the “obesity epidemic” but can they also be possibly accused of contributing to the problem we so ardently wish to solve(1)?
The dietary advice to prevent obesity used to emphasise the central issue – not eating too much. Recently, for reasons that may have nothing to do with obesity and everything to do with selling new food products, attention has shifted to the choice of foods, rather than the overall amount. Huge advertising and promotion budgets are put behind every new product launch, in order to hammer home the message “This product will make you healthier, feel more energetic”. The trouble is that whatever the benefits or otherwise of all those low-fat products for us adults, for young children they may have exactly the opposite result to that intended. The reason now seems clear – it is too much protein(2). By one year of age, the average baby is eating three times as much protein as they need. Yet a lot of worry seems to hover over giving advice on weaning diets for babies and whether they are getting enough protein(3). As a result, infants and young children are being fed far more protein than they need.
The impact of early nutrition on subsequent growth and disease is neatly described as “programming”. What happens to a child before the age of two can be seen to influence their growth, weight and health for many years afterwards. Population studies suggest that early life influences later obesity risk in some way(4). Babies fed a high-protein diet show increased levels of growth stimulating hormones(5). Apart from early obesity, another affect of a diet too high in protein seems to be early maturation. This can lead to disadvantages for the child. Early menarche in girls is associated with an increased risk of subsequent breast cancer, for example. It can even affect their own children, especially if a girl has a baby while still a teenager.
Several lines of evidence have now come together to suggest that a radical re-think of the dietary advice given to parents for their infants may be long over-due. For many years it was believed that the under-nutrition so prevalent in the poorer countries of the world was essentially due to a shortage of protein. When it also became clear that, if true, this shortage represented a net under-production of protein in the entire world, huge campaigns were launched to increase world protein production by any practicable means. Only later, was it discovered that this theory was incorrect. The under-nutrition seen in the third world was shown to be primarily a shortage of calories, not protein(6). Hence the starvation formerly known as “protein malnutrition” was re-named “protein energy malnutrition”.
There is now serious reason to believe that the pendulum has swung too far away from fat and carbohydrate, in favour of protein. The evidence is persuasive. First, we have the fact that a baby’s body weight and growth in the first year or two of life have been shown to predict later risks of heart disease, diabetes and cancer(5). Rapid growth in height at an early age was traditionally seen as a good sign, indicating ideal nutrition, especially if associated with low body fatness. Recent evidence suggests the exact opposite: that these are signs of inappropriate nutrition. The rapid growth in body length (height) is a sign of too high a protein intake; the low body fatness, a sign of inadequate calorie consumption, caused by the ability of protein to make the child feel full before it has consumed enough food energy. The subsequent experience of a child with these characteristics at age two will usually be continued growth in height but also in fatness, leading to an overweight teenager who is both fat and tall.
A second line of evidence suggesting too much protein in infancy is causing, at least some of the current problems of obesity in children, is the observation that babies fed with formula milk, rather than breast milk, tended to be heavier, both as babies and later as children and adults. Formula milk used to be richer in protein than breast milk, in the belief that this was a good thing. Recently, the composition of formula milk has been changed to reduce its protein content to the same level as breast milk. A careful study has now shown that babies fed with the revised recipe formula milk become no heavier than breast fed babies, confirming the importance of protein in influencing body weight in this age group(7).
The third line of evidence is the most convincing. Careful dietary surveys have been conducted on children’s eating and exercise habits over nearly two decades of their lives, from weaning as infants until they reached early adulthood at age twenty. These surveys were expected to reveal differences in the eating habits of those who became overweight. Conventional wisdom suggested the tendency to put on weight would be associated with overconsumption of fat and sugar. In fact the only discernable over indulgence was in protein early in life, at an age where the choice of food would have been the mother’s choice on behalf of their infant child(2). Many low fat products, especially dairy products such as yoghurts, are commonly low in sugar too, and are very popular with young children. They are, however, very high in protein. The result is an overall diet high in protein, stimulating early growth in height, early maturation, and later overweight problems.
Breast milk is high in fat (52% of calories) and carbohydrate as sugars (42%) but low in protein (5%). And yet, the typical diet of a one year old infant today contains only about 28% of calories as fat and a massive 16% as protein. As the child gets older its fat intake will typically rise to about 36% and its carbohydrate consumption will settle around 47% (comprising partly starch and partly sugars). Protein intake, on the other hand will remain much the same, and much higher than requirement.
This was not the pattern of nutrient intake seen in the past. Surveys over the last thirty years have shown, for example, a substantial decline in consumption of whole milk among children as young as two, with a corresponding increase in consumption of low fat milks. This is despite repeated advice from experts not to impose adult low fat diets on children at this age. Such a change in milk consumption, at an age when milk is a major food energy source, will have the effect of increasing protein intake while reducing fat, and therefore calories. The result is children’s calorie intake falling over time, which would be expected to lead to a reduction in obesity during later childhood and adolescence. In fact the opposite has occurred: the proportion of children who are overweight has soared.
The implications of all this research are clear. Young children should not be transferred onto an adult diet at too early an age. The transition from the low protein, high fat, high carbohydrate diet of breast milk to the moderate protein, moderate fat, and high carbohydrate intake recommended for adults should be phased gradually over the first five years of life. It should not be introduced abruptly during the weaning process. Equally, a weaning diet that is too high in protein may exacerbate the “programming” effect of a high protein intake from the formula milks used for bottle feeding babies in the past.
The over-zealous exclusion of fat and sugar from a young child’s diet can have serious disadvantages for their development and health in later life. It is possible to have too much of a good thing – in this case protein. Children need energy. Their diet must provide that energy without excessive protein intake. The major sources of energy for children, as for adults, should be carbohydrate and fat. The main carbohydrate source should be starches. A moderate intake of sugars at meal times, coupled with the all important introduction of fluoride tooth paste from the time when the first teeth begin to erupt (around six months of age), will help to encourage good dietary habits and healthy teeth. Frequent between-meal snacking, on any carbohydrate food, should be avoided, because of the risk of tooth decay.
Fat is essential to the taste and palatability of many foods. We should all be able to enjoy our food, whatever our age. In addition, especially during early childhood, fat is an important source of necessary energy, when bulky, low-fat foods may not provide enough calories for a child’s small stomach. Current advice would emphasise the quality of the fats consumed by young children, rather than the quantity. Protein intake should also be limited but of high quality.
References
- Marantz PR, Bird ED, Alderman MH (2008) A call for higher standards of evidence for dietary guidelines. American Journal of Preventive Medicine 34:234-240.
- Rolland-Cachera MF, Deheeger M, Maillot M, Bellisle F (2006) Early adiposity rebound: causes and consequences for obesity in children and adults. International Journal of Obesity 30:S11-S17.
- Department of Health Weaning and the weaning diet. Report on Health and Social Subjects 45. Report of the Working Group on the weaning diet of the Committee on medical aspects of Food Policy. HMSO, London 1994.
- Olsen LW, Baker JL, Holst C Sorensen TIA (2006) Birth Cohort Effect on the Obesity Epidemic in Denmark. Epidemiology 17: 292-295.
- Stern MP et al (2000) Birth weight and the metabolic syndrome: thrifty phenotype or thrifty genotype? Diabetes/Metabolism Research and Reviews 6: 88 -93.
- Waterlow JC and Payne PR (1975) The Protein Gap Nature 258: 113-117.
- http://earnest.web.med.uni-muenchen.de/obesity/results.htm
