Dr Barnard is president of the Physician's Committee for Responsible Medicine and one of America's leading health and weight-loss experts. In his book, he claims that certain foods boost your cells' ability to turn more of what you eat into energy, not fat.
Metabolism, he explains, is the process of turning fuel - that is, the glucose that comes from the food you eat - into energy. If you have a fast metabolism, you burn lots of calories all the time. The faster your metabolism, the faster you burn up calories, and the less fat you store.
And while most people think you have to exercise to speed up your metabolism, according to Dr Barnard you can just do that with the food you eat. By choosing the right foods, he says, you can reprogram your cells to speed up your metabolism after every meal.
One of the studies Dr Barnard describes in his book involved a group of volunteers who were asked to eat mainly plant-based meals (that is, very little fish, dairy and meat), and to keep oils to a minimum for a few weeks. On testing them after the study period had ended, Dr Barnard found their after-meal calorie burn was bigger - in other words, they were converting more food into energy instead of storing it as fat.
On average, he says, the volunteers were burning calories about 16% faster than previously and for about three hours after eating. That might not sound particularly impressive, but if you can do that three times a day with each meal you eat, it all adds up.
How to do it
So what are the eating principles behind Dr Barnard's metabolism-boosting theories?
1. Eat lots of fibre
According to Dr Barnard, fibre is metabolically active, plus it helps reduce your appetite. When it's in your stomach it holds water, so it tricks your stomach into thinking you've eaten a lot - yet it contains virtually no calories.
Plant foods contain fibre, including whole grains, beans, pulses, fruit and vegetables. There is no fibre in meats, dairy products or eggs.
So, for instance, if you want to make chilli, skip the meat and cheese and make it with beans, tomatoes and vegetables instead. Similarly switch cream-based soups for vegetable or lentil varieties, and chicken salad for chickpea salad.
2. Skip fatty foods
It pays huge dividends to avoid fatty foods, says Dr Barnard. And that means skipping animal products, since he claims most of them have more fat than is healthy. Also be careful about vegetable fats, including added oils, fried foods and oily salad dressings, as well as nuts, seeds, olives and avocados.
So instead of a breakfast that includes two fried eggs, two strips of bacon, buttered toast and hash browns, you could have wholewheat pancakes topped with blueberries and maple syrup, with two strips of veggie bacon. Interestingly, the second breakfast may sound like it has more calories, but according to Dr Barnard it actually has 50 fewer cals.
3. Eat low-GI foods
Foods that are high on the glycaemic index (GI), such as white bread, are not going to make your metabolism work faster, so stick to low-GI foods. For instance, replace sugar (high GI) with fruit (most are low-GI), white or wholewheat bread with rue or pumpernickel bread, white potatoes with yams or sweet potatoes, and cold cereals with porridge oats.
• The 21-Day Weight Loss Kick Start Diet by Dr Neal Barnard is published this month, priced £12.99
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