At the tail end of 2012, I wrote a blog post about the impact of emphasising fruit and vegetables in the diet. ‘Filling up of fruit and veg’ is often recommended as a weight loss tactic. But, as I explained in the blog post, I’m not sure this is good advice at all. I argued that the fundamental problem is that, for the most part, people tend not to find fruit and veg particularly filling and/or sustaining. Because of this, adding more fruit and vegetables into the diet does not necessarily translate into a reduction in the overall amount people eat.
In fact, in the blog post I report on a study in which both lean and overweight individuals were asked to emphasise fruit and vegetables in their diet, to see its effect on satiety and latency (the amount of time it takes before someone want to eat again) and overall food intake [1]. In short, what the study showed is that eating more fruit and veg did not lead to people eating less (in caloric terms) overall. Actually, the overall effect was for them to eat more and gain weight.
I was interested to read a related review published this week in the American Journal of Clinical Nutrition [2]. In it, US researchers collated evidence from a range of studies in which the emphasising of fruit and vegetables had been recommended to individuals with the goal of weight loss. A total of 7 studies were included as part of the review. The conclusion was that the studies simply do not support the proposition that adding more fruit and vegetables to the diet aids weight loss.
Why does fruit and veg fail to sustain? Well, while these foods can offer useful nutritional offerings (e.g. vitamins and other nutrients), they tend not to be rich in certain other elements that are essential to health including ‘essential amino acids’ (from protein) and ‘essential fats’. In essence, maybe the body knows that fruit and vegetables are lacking in dietary elements that are critical to our survival.
There is also some evidence that protein is the most sating and sustaining element of the diet (compared to carbohydrate and fat), and I certainly see evidence of this in the real world. This is one of the reasons why when talking to non-vegetarians, I recommend meaty soups over vegetables ones, and that if someone is going to eat a salad “it helps if there some animal in it.” Leaving aside the nutritional attributes of protein and fats in animal foods, the end result of eating these sorts of meals (as opposed to their ‘lighter’ versions) is usually that people feel more satisfied after eating (so perhaps less tendency to eat something else like cake, chocolate or crisps/chips straight after), as well as a feeling that they can go for longer without hunger biting again.
Fat, for some people, does seem to have some important sating properties. I’ve come across many individuals who will, for instance, not feel as sustained after eating a chicken breast as after eating a single chicken leg. The sating effects of protein and fat have been seen in a study which found that lower–carb diets lead to a significant spontaneous reduction in calorie intake, and that the more fat is eaten, generally the less is eaten quite naturally [3].
While this may not apply to all, I generally find that if people want to eat less without hunger, then some emphasis generally needs to be placed on foods rich in protein and fat. To be honest, for most people, fruit and veg just does not cut it.
References:
1. Houchins JA, et al. Effects of fruit and vegetable, consumed in solid vs beverage forms, on acute and chronic appetitive responses in lean and obese adults. Int J Obes advance online publication 2013;37(8):1109-15
2. Kaiser KA, et al. Increased fruit and vegetable intake has no discernible effect on weight loss: a systematic review and meta-analysis Am J Clin Nutr 2014 First published online 25 June 2014
3. Johnstone AM, et al. Effects of a high-protein ketogenic diet on hunger, appetite, and weight loss in obese men feeding ad libitum. AJCN 2008;87:44-55
