High-carb or high-fat: which way should we lean and why

Arguments continue about which end of this spectrum is healthier but the results of a recent study give us strong clues.

High-carb diets are low in fat, and among the claims made by people who advocate this way of eating is that it keeps us slimmer because fat contains 9 calories per gram while carbs contain only 4.

The high-fat side points out that those extra carbs increase blood sugar and insulin, which encourages fat storage and hunger.

So who’s right?

American researcher Kevin Hall recently compared the impact of these two dietary regimes on 20 young people aged around 30 — 11 men and 9 women with stable weight.

While I’m calling these diets high-carb and high-fat, bear in mind that high-carb diets are also low-fat, and high-fat diets are also low-carb.

To be specific, Hall’s team were comparing what they called a plant-based low-fat diet (in this case vegan and high-carb) with an animal-based ketogenic (i.e. high-fat) diet.

For 28 days the study participants lived in a research clinic where they were randomly assigned to follow one diet for the first fortnight then switch to the other one for the second fortnight. On each diet they could eat as much or as little as they liked.

It’s expensive to house and feed 20 people for a month but it’s one way to really know what they’ve eaten.

While protein remained constant at 15% of calories in both cases, the high-carb diet was 75% carbs, 10% fat and the high-fat diet was the opposite — 75% fat, 10% carb.

The high-carb vegan meals included, for example, instant rolled oats with blue berries, vanilla soy milk and banana for breakfast; lentil and basmati rice soup with vegies for lunch; and pasta salad with fat-free dressing (and sliced apple dessert) for dinner.

Typical high-fat meals were scrambled egg (including cream) with vegies for breakfast, roast beef salad plus shredded cheese and guacamole for lunch, and baked salmon with buttered green beans and almonds for dinner.

What the researchers wanted to know was how many calories the participants would eat on each diet and whether they’d have less appetite when they ate fewer carbs.

It turned out they lost weight on both diets.

On the high-carb diet participants burned more calories than they ate, so we’d expect them to lose weight. After two weeks they lost about 1.09 kgs.

But here’s what’s interesting. On the high-fat diet people ate more than they burned up and still lost about 1.77 kgs. Huh?

While there’s not much difference between the two regarding the amount lost, this flies in the face of the idea that weight loss is about burning more calories than we eat. There’s clearly more to it than that.

On the high-carb diet people ate about the same number of calories in weeks one and two, but on the high-fat diet they ate a bit less in week two.

On a high-fat diet our bodies need to adapt to using fat rather than carbs for fuel. The vast majority of us run on carbs and the switch-over to fat can take a few weeks.

It’s possible that the lower calorie intake in week two was a reflection of that starting to happen as the participants’ bodies adapted to needing less food.

But we don’t know. The study didn’t go long enough to see what might have happened in subsequent weeks.

Another important point here — and the problem with the ‘calories in vs calories out’ theory — is that not all calories are equal.

Proteins, fats and carbohydrates perform different jobs in our body. Protein builds and maintains tissue, protein and fat regulate bodily processes (such as clotting blood or absorbing vitamins and minerals), and carbs and fat provide energy.

When we’re older our bodies have a greater need for nutrients that build and maintain and keep us functioning well, and less need for straight out energy. So it makes sense to eat a diet that contains good quality protein and fat and not too many carbs.

Remember too that most of us absorb animal protein better than plant protein. In addition, vegan diets can also be deficient in vitamins such as B12 and D, minerals such as iron and zinc, and omega-3 fats.

In Kevin Hall’s study the animal-based ketogenic diet was nutritionally superior to the vegan one. One explanation for the people on the ketogenic diet eating more calories than they expended but still losing weight is that it provided enough nutrients to meet the participants’ metabolic needs, whereas the high-carb diet didn’t.

As anticipated, the high-carb diet also produced more insulin. Chronically high insulin underlies diseases such as type 2 diabetes, fatty liver disease, heart disease and Alzheimer’s.

Of course, most of us don’t eat strictly high-carb vegan or ketogenic diets. But culturally our habits tend towards the high-carb end of the spectrum — breakfast cereal, pasta, rice, processed snack foods, bread, sugar, sweeter fruits, alcohol, and so on.

After menopause, we have less estrogen. Since estrogen is anti-inflammatory, in post-menopause our bodies are more prone to inflammation. Adding an insulin-boosting (i.e. inflammatory) diet on top of that just ups the ante.

If we’re not overweight and don’t have chronic disease we’ve probably got more leeway, but if we’re carrying fat around our middle or have early signs of disease (such as high blood pressure) it’s worth looking at where we could reduce our intake of these kinds of carbs.

Even though grain-based foods are often promoted as ‘healthy’, one small 30 gram slice of isolation sourdough is equivalent to four teaspoons of sugar in your blood stream. Most breakfast cereals are equivalent to the same or more.

I’m not saying we should all be on ketogenic diets. At the very least that’d be unsustainable for most of us. But this research reinforces the merit of steering a little more towards good quality protein and fat with fewer carbs.

A Canadian nutrition counselling company recommends substituting greens for grains. It mightn’t work for your breakfast cereal but it’s a strategy for lunches and dinners — salad and vegies instead of rice, pasta and bread.

Taking up from last month’s post about the two older people’s approaches to COVID eating, this means taking a leaf out of Peter Brukner’s dietary book rather than Jane Brody’s.

Photo Source: whatthefatbook.com