Anyone who has tried to lose weight has probably followed a number of different diets. 5:2, The Paleo Diet, high protein, low GI diet or meal replacements – what is a dieter to choose?
I was interested to find out which of these diets actually have hard scientific evidence, or whether it’s all in the marketing hype. Last week, the British Nutrition Foundation held a conference in London with an impressive line up of distinguished academics, looking at the evidence for each.
Here is a brief summary of the fascinating presentations:
The Fasting Diet
You can’t fail to have heard of 5:2. ‘Fasting’ isn’t strictly true as it’s about having a very restricted intake (500 – 600 calories/day) on two days a week or alternate days – rather than no food.
Fans of this approach say that because you only need to be really strict about what you eat 2 days a week rather than every day, it’s more manageable.
I was surprised to discover that only two studies – one in the UK and one in the US, both with women, are behind the huge range of 130+ books on the subject. The research was looking into whether this way of eating had cancer preventative benefits, not weight loss. Participants had a restricted calorie intake on 2 days (UK study) or alternative days (US study). A very important point was that participants were also eating fewer calories through a mediterranean style diet on the non-fasting days (1350 – 1450 calories a day). So they were consuming significantly fewer calories across the whole week.
Does it work?
If your calorie intake over the week is reduced, then yes, you will lose weight. But a concern is that some people are under the impression that you only need to restrict your food intake on ‘fasting days’, then you can eat what you want for the rest of the week. This is not what the research showed. The reality is that it is very much the quality of what you eat and quantity on non-fasting days that affects weight loss.
The Paleo (‘caveman’) Diet
The idea is to eat like our hunter /gatherer ancestors. There is a misconception that the caveman’s diet was full of red meat (hence why the Paleo Diet has a lot of male followers), but the reality is that our ancestors ate a huge amount more fresh fruit, berries and vegetables than we do– up to 100 different plant-based foods per year! Meat may not have been available everyday – it depended on what they could hunt. Location would have also played a part – for example coast-dwelling people probably ate more fish than meat.
A true Paleo meal is full of bulky veg, high in fibre and low in starch, making it very filling but low energy density (in calories). Fruit and vegetables contain compounds called phytonutrients (these are in addition to vitamins and minerals). Evidence showed that when different combinations of plant-based foods are eaten together, the phytonutrients work together to control the spike in the blood glucose after a sugar-rich meal, controlling how much glucose is absorbed into the body.
Interestingly, older varieties of our favourite crops have more phytonutrients than many grown today. The emphasis now is on planting foods that give the biggest yield, not for nutrient content, so it does seem that the focus on mass production may be at the expense of getting more phytonutrients in our diet.
Does it work?
The true principle of this diet is about eating a lot more fruit and veg than we do now. 5-a-day is only a starting point. Not just the same old fruits and veggies each week, but a real variety.
Eating bulky meals packed full of vegetables that are high in fibre and low in calories will most certainly help you feel fuller. Combined with eating more lean protein, whole grains and less processed food, you are going to be eating a very healthy diet. The more satisfied you feel and the more even the release of energy into your bloodstream, means you are less likely to get energy dips that can lead to cravings. As long as your calorie intake is reduced, you will lose weight.
The speakers went on to present the evidence for three more types of diet. My summary:
High protein diets – are a useful weight loss tool but should not be treated as a diet for life (health concerns).
Low GI – proven to help with diabetes type 2 management but has mixed evidence for appetite and body weight; principle is good but measurement is challenging, as is consuming the amount of fibre required.
Very Low Calorie Diets – can achieve rapid weight loss for people who need to lose weight fast for health, but unless healthy eating is understood, weight gain is likely when ‘real food’ is reintroduced.
What to be aware of
Limitation of studies. All of the academics presenting pointed to the need for more research to build on the knowledge gained so far.
Comparing animal responses to humans. Behaviours are not always translatable.
Intervention affects behaviour. Reporting in to someone and being monitored will affect how a participant complies with a trial.
The power of the media. What struck me was how in some cases, fairly small studies are behind such huge diet crazes.
What’s critical to the success of any diet is how manageable it is – can you stick with it? As we are all individuals we will be drawn to different weight loss approaches. There is certainly not one ‘diet’ that fits all, it is ‘horses for courses’.
The one last and vitally important statement from one academic was…
These diets are simply tools to help. Weight loss is fundamentally down to the law of thermodynamics – energy consumed must be less than energy burned. Regardless of what food you eat.
Our food diary helps you measure energy in and out. To keep it simple, we focus on calories and total fat. This is why.
If you follow the principles of these popular diets, you actually don’t need to juggle with monitoring anything else. We give you a calorie target (roughly 25% reduction), so if you stick to this target and follow the healthy eating tips below, you will naturally be eating less sugar, salt, and saturated fat and more fibre, protein and ‘good carbs’.
What to eat based on the evidence
- A HUGE variety of fruit and veg. Forget 5-a-day, aim for 10-a-day! Look for older varieties.
- Include some protein in each meal. Mix it up – fish, soya, meat and dairy.
- Choose complex, unprocessed carbohydrates – brown rice, wholegrain cereals, whole wheat pasta, pulses (lentils, baked beans, kidney beans, broad beans, butter beans, peas )
- Fluctuate your daily calorie intake a little if you wish to (your food diary lets you do this) but there’s no need to go for serious restriction on specific days as long as you achieve a calorie reduction over the week.
So it seems that these diets all lead us back to the same place: to lose weight, you should eat a healthy, balanced calorie reduced diet. Simple. But perhaps not as exciting and promising as the latest new diet.
To hear the conference yourself, go to the link on the British Nutrition Foundation website: http://www.nutrition.org.uk/bnfevents/pastevents/populardiets