strength training diet

Strength Training Diet : Hormones and strength - why low-fat, high-protein diets might not be best after all

At a glance:

  • Low-fat, high-protein nutrition has long been considered as ‘de rigeuer’ for strength athletes;
  • But a new study indicates that higher fat and lower protein intakes are associated with increased levels of muscle-building anabolic hormones in strength athletes;
  • Some research also indicates that dietary fat may help the body’s anabolic hormones to work more efficiently;
  • These potential benefits may be associated with meat consumption, but more research is needed.

Years of careful research and scientific studies seem to point to the unavoidable conclusion that a low-fat diet containing ample protein provides the best nutritional environment for strength athletes. But now some surprising new research suggests that this view may be oversimplified, writes Andrew Hamilton.

Scan the ingredients list of any tub of weight gain powder and it’s easy to see the current thinking on nutrition and strength building. While the brands may differ, the contents are strikingly similar; all are invariably high in protein, low in fat, with varying amounts of carbohydrate. The reasoning is simple: dietary protein provides the source of amino acid building blocks needed by your body to synthesise new muscle tissue, as well as to replace and repair tissue broken down during exercise itself.

Although the exact protein requirement for athletes remains the subject of debate, the consensus among sports nutritionists is that athletes do need more protein for optimum performance and recovery than their sedentary counterparts. In fact, the research suggests that athletes engaged in intense training actually need to ingest about 1.5-2 times the normal RDA for protein in order to maintain a positive protein balance (1-5). This equates to 105-140g of protein per day for a 70kg athlete.

Fifty years ago, high protein steak and egg diets were the order of the day. The thinking was simple: muscles are made of protein, therefore to develop muscular strength requires a large intake of protein. However, as the understanding of carbohydrate metabolism and sports performance grew, scientists began to realise that this approach was grossly oversimplified. That’s because we now know that the uptake of amino acids into muscle cells is strongly regulated by hormones.

One of the most anabolic (ie muscle-building) hormones in the body is insulin, which is released whenever carbohydrates are eaten. The primary job of insulin is to regulate the amount of glucose in the blood that results from eating carbohydrate, by stimulating cells to take up glucose.

However, this release of insulin also has a potent anabolic effect, helping to drive amino acids into muscle cells, thereby stimulating muscle protein synthesis. In fact, research has demonstrated that feeding protein plus carbohydrate to promote an insulin release results in 50% greater muscle protein synthesis than feeding protein alone (6).

But carbohydrates also play another valuable role in muscle metabolism – that of helping to conserve hard earned muscle tissue. While a high- protein diet provides plenty of amino acid building blocks to build muscle protein, unless there’s sufficient carbohydrate present to support training (remember, carbohydrate is the body’s ‘premium grade’ fuel for exercise), these amino acids are simply used to supplement the fuel supply.

A low-carbohydrate diet combined with vigorous exercise therefore results in protein oxidation for energy, and since muscles are the major store of amino acids, this can result in muscle tissue loss, especially when training volumes are high.

Moreover, research has clearly demonstrated the importance of ample dietary carbohydrate in reducing the amount of catabolic stress hormones, such as cortisol and adrenaline, which are released during and after exercise and which stimulate the breakdown of muscle tissue (7,8,9). In short, carbohydrate is as much a part of the anabolic equation as protein.

The protein/fat equation

Given that both protein and carbohydrate are needed for muscle growth and maintenance, it’s easy to understand how the consensus that high- protein/ample-carbohydrate/low-fat diets are best for strength athletes has arisen. A diet containing moderate or high levels of fat and plenty of protein/carbohydrate would necessarily contain a lot of extra calories, especially as each gram of fat provides 9kcals of energy – double that of carbohydrate or protein. And as we know, an excessive calorie intake leads to gains in body fat – exactly what most athletes don’t want.

Meanwhile, a calorie-controlled moderate/highfat diet would necessarily have to contain relatively little protein and carbohydrate – again not desirable for an athlete seeking to maintain or build strength. Together, these facts explain why protein is king, and why (not withstanding the growing realisation of the importance of essential fatty acids) fat is almost seen as a dirty word among strength athletes.

Gaining and retaining muscle tissue certainly requires ample protein and carbohydrate, but that’s not the whole story. After all, if it were, consuming larger and larger quantities of protein would lead to ever increasing strength and muscle size – something that obviously doesn’t happen. This is because hormones also control the metabolism of muscle tissue and protein turnover. Naturally occurring anabolic hormones such as testosterone and human growth hormone (HGH) act as chemical messengers, directing muscle cells to take up amino acids and synthesise muscle protein. They also stimulate the oxidation of fat for energy, thereby increasing lean muscle mass while decreasing fat mass.

The action of anabolic hormones is balanced by ‘catabolic’ hormones, such as adrenocorticotrophic hormone and cortisol. These hormones are released during ‘fight or flight’ situations, where energy production becomes paramount, and tend to produce a breakdown of body tissue. Building or maintaining strength requires a hormonal balance that is more anabolic than catabolic. This explains the illegal use of anabolic steroids, substances that artificially boost anabolic hormone levels (see box below).

Anabolic steroids as drugs

Anabolic (or more correctly, androgenic-anabolic) steroids (AAS) form a family of synthetic drugs derived from the male sex hormone, testosterone, and are used to promote muscle growth and increased lean body mass. Although they have many approved medical uses, steroids are sometimes abused by athletes seeking to improve performance.

However, the non-medical use of these drugs carries severe physical and psychological health risks. In males, they can trigger a mechanism in the body that leads to the shut-down of the healthy functioning of the male reproductive system, resulting in a number of effects, including shrinking of the testicles, reduced sperm count, impotence, premature baldness, enlarged prostate gland and enlarged breasts (gynecomastia).

In females, effects include deepening of the voice, the growth of facial hair and reduction in breast size. More generally, other symptoms are commonly observed, including severe acne, weakened tendons (leading to increased injury risk), severe mood swings, uncontrolled bursts of anger, delusions and paranoia and depression (especially when steroid use is discontinued). The longer-term health effects include increased blood pressure and cholesterol, leading to an increased risk of heart disease, as well as kidney and liver disease.

But can hormonal balance be influenced by nutrition? Leaving aside the issue of exotic sports supplements such as pro-hormones, new evidence has emerged that suggests that protein and fat ratios can impact on hormonal balance, but in a rather surprising way.

A joint Finnish and American study examined the relationship between dietary intake patterns and the resulting blood concentrations of the anabolic hormones testosterone (T), free testosterone (FT) and growth hormone (10).

In this study, eight strength athletes and 10 physically active non-athletes were examined at rest as well as after heavy-resistance exercise. During the first part of the study, all the subjects were allowed to eat freely, but kept detailed food diaries. The scientists then examined how these differing dietary patterns affected the levels of hormones in each of the subjects . In the second part of the study, a sub-group of five strength athletes and five non-athletes kept diaries for a further four days before undertaking a high- volume, high-intensity resistance workout.

What the scientists found surprised them. During the non-active period, a higher fat intake and lower protein intake was associated with increased levels of anabolic hormones across both groups of subjects.

However, during the phase of the study containing the high-intensity resistance exercise, this correlation disappeared for the non-athletes, but remained for the trained strength athletes – ie higher fat intakes and lower protein intakes were associated with increased blood levels of anabolic hormones in the strength athletes only. The clear implication is that the role of diet in producing a favourable anabolic environment may be more important for trained athletes.

The researchers went on to conclude that ‘the results suggest a possible link between diet and changes in blood hormones during prolonged strength training, and that diets with insufficient fat and/or excessive protein may compromise the anabolic hormonal environment over a training programme’.

Fat and growth hormone

The fact that a higher dietary fat and lower protein intake appears to increase anabolic hormone levels, especially in trained athletes, seems counterintuitive and flies in the face of conventional wisdom. But while more research is obviously needed in this area, some other studies also hint that the low-fat, high-protein route may not be quite the holy grail we all thought it was.

In one of these studies, the interaction between fat metabolism and muscle-building growth hormone was examined (11). To do this, the subjects fasted for 37 hours in order to suppress their natural production of growth hormone (GH – suppression of growth hormone normally occurs during fasting). They were then infused with one of the following:

  • GH alone;
  • GH together with a drug called Acipimox, which blocks the release of fat from fat stores and fat metabolism;
  • No GH with Acipimox;
  • GH with Acipimox plus extra lipid (ie to provide the body with an extraneous source of fat).

As expected, urinary urea excretion, blood urea and muscle protein breakdown (all are measures of protein catabolism in the body) were increased by almost 50% during the fast when fat metabolism was being suppressed.

Giving extra GH alone reduced the rate of muscle loss during the fast, but when the subjects were also being infused with Acipimox, extra GH didn’t reduce the rate of muscle tissue loss. However, when fatty acids were then added to the infusion (to provide a source of fat), the rate of whole body protein degradation dropped to just 15% above baseline values (ie the GH was able to exert an effect again), providing strong evidence that fatty acids in the bloodstream are important protein-sparing agents during fasting. The implication is clear; fat seems to play a decisive role in the process of protein conservation during fasting in humans, possibly by helping growth hormone to work more efficiently.

Another fascinating study examined the effect of meat-containing diets and vegetarian diets on strength and body composition when combined with resistance training (12). In this 12-week study, 19 men were split into two groups:

  • Ten subjects were instructed to continue consuming their normal omnivorous diet (containing a mixture of protein sources including meat) while the resistance training was continued;
  • The remaining nine men were counselled to select a lacto-ovo vegetarian diet (ie exclude all meat) for the duration of the study.

All of the subjects kept food diaries, and while carbohydrate, protein, nutrient and alcohol intakes were not significantly different between the two groups, those on the meat diet tended to consume more fat.

Once again, the results confounded the researchers. Although the 12-week resistance training programme produced the same gains in maximal strength (10-38%) in both groups of men, the changes in body composition and skeletal muscle size were significantly different. The meat eaters gained an average of 1.7kg of lean muscle, while the vegetarian group lost an average of 0.8kg. Moreover, the meat group lost an average of 1.3kg of fat, while the vegetarian group actually gained 0.1kg.

Although the researchers cautioned that the food diary methods they employed could not be considered 100% accurate, they did conclude that there was a real difference between the two dietary patterns. The exact cause(s) for this difference remains unclear and, once again, more research would be needed – for example to investigate whether it was the higher fat content of the meat diet per se that produced these results, or some other factor.

One possible reason advanced by the scientists was that the meat diet may have produced higher levels of the muscle-building hormone testosterone, a phenomenon that has been observed in endurance athletes (13). Eight male endurance athletes were split into two groups and put on either a lacto-ovo vegetarian diet or a mixed, meat-rich diet. However, the diets were formulated so that the protein/fat/ carbohydrate ratio was kept pretty much the same (58%/27%/15% on the vegetarian diet and 58%/28%/14% on the meat diet). After six weeks, the groups were reversed, ie those on the meat diet switched to the vegetarian diet and vice versa.

A balancing act in the body; anabolism vs catabolism

The body is in a constant state of flux, building up and breaking down tissue as required. This requires a careful balance of anabolism (tissue synthesis) and catabolism (tissue breakdown).

Naturally occurring anabolic hormones include:

human growth hormone

IGF1 and other insulin-like growth factors



oestrogen (although associated with feminising characteristics, it’s an anabolic hormone).

Naturally occurring catabolic hormones include:



adrenalin and other catecholamines


Other hormones are intimately associated with maintaining the correct balance of the catabolic and anabolic states, such as orexin and hypocretin (which function as a hormone pair) and melatonin (derived from serotonin), which plays a role in sleep, ageing and reproduction in mammals.

The researchers discovered that, compared to the vegetarian diet, consuming the meat diet produced significantly higher levels of the anabolic hormone testosterone. They also noticed that the endurance performance time was better for more of the athletes after the meat diet than after the vegetarian diet, although these differences were not large enough to be considered statistically significant.


Do these findings mean that sportsmen and women should abandon the currently accepted nutritional wisdom and switch to higher-fat, low-protein diets? Of course not! However, these studies perfectly illustrate the complexities of formulating optimum eating regimes for athletes. In particular, they suggest that the practice among some athletes of following extremely low-fat diets, or eschewing all red meat from the diet on the grounds that it contains more fat than other protein sources, may actually be counterproductive. Much research remains to be done, but in the meantime it seems that a little of what you fancy really may do you some good.

Andrew Hamilton BSc, MRSC, trained as a chemist and is now a consultant to the fitness industry and an experienced science writer


  1. J Appl Physiol 1992;73(2):767-75
  2. J Appl Physiol 1988;64(1):187-93
  3. J Appl Physiol 1992;73(5):1986-95
  4. Curr Opin Clin Nutr Metab Care 1999;2(6):533-7
  5. Sportscience 1999;3(1) Available:
  6. J Clin Invest 1995;95:811-819
  7. Int J Sport Nutrition 1998;8:49-59
  8. Journal of Applied Physiology 1998;84:1917-1925
  9. International Journal of Sports Medicine 2001; 22:226-231
  10. Int J Sports Med 2004 Nov;25(8):627-33
  11. J Clin Endocrinol Metab 2003;88(9):4371-8
  12. Am J Clin Nutr 1999;70(6):1032-1039
  13. Med Sci Sports Exerc 1992;24(11):1290-7

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